I just discovered that a member of my extended sim-family died. They are not my active household and I have no idea when this occurred since I haven't played this particular game since early last month and somehow I missed the announcement. (certainly understandable since sometimes I close out those constant updates without fully reading them all, even with SP set to just just family and friends it can be a lot)
Anyway, so two of my sims (a brother and sister) are married to two brothers who live in my active family's mansion. (they auto-hooked up as teens so I just went with it) It's the brothers sister who died, by drowning based on her blue-drippy ghost. Since I've only ever saved a sim ghost once i thought this was a great opportunity to try again since we have all the stuff for Ambrosia in our fridge! So I found her tombstone in the mausoleum and brought it to the house. It appears she and her brothers are still close, since they chatted with her ghost and the relationship bar is full for both brothers. So I made a plate of Ambrosia and it is sitting at her grave, but she's not even attempted to eat the darn stuff! We are on day 3 of her haunting the house and I've tried clicking her, but I don't get an option to make her active or have her join the household or anything so I'm not sure how to get her to eat!
The one time I did save a sim with Ambrosia every ghost in the graveyard went for the plate so this time I did it on my active lot, but she's ignoring it and either playing the piano or haunting stuff. Is it too late to bring her back or do I just need to be more patient?

Easiest way imo: resurrect them at the science lab to make them playable and then have them eat the ambrosia.

I can't get them to the lab, there's no option for this. I put the tombstone in either brother's inventory, click the science lab and there's no option about bringing them in. Besides I think that only works if your sim died on the lot and you have to get them in during that window of opportunity some time right after death. Or if a sims works there they sometimes offer the opportunity, but this sim is already a ghost and the brothers have talked to her. She just wont eat the Ambrosia, perhaps she just prefers being dead. ?? ;-0

You know, being dead isn't as bad as it sounds. You don't have to worry about eating or sleeping, or getting a job for that matter, you can come and go as you please, people won't bug you when you'd rather not deal with them, and when your uncle starts talking politics at the dinner table in front of your very indignant mother, you can just... float away. (Okay, maybe that last one is just for me.)

To get the science lab to resurrect a sim, you need to be offered the Oh My Ghost opportunity. It's in the special category. You can use MC to assign it: NRaas > MC > Basic > Opportunity: By Category. I've never accepted this, so I don't know how it works, or even if it works once a ghost has appeared. I'm also not sure what to do if the opp doesn't show up in the menu; with Opportunity: Random, it seems like it could take a while to cycle through all the potential options.

I suppose you could also try an Add Sim command: MC > Household > Add Sim > (select the ghost; you can sort by current lot if she's around). But be sure to have a backup in case this somehow borks your game.

puzzlezaddict - LOL thanks! Perhaps she will just eat the darn stuff eventually, or perhaps I will try something else. I don't really care that much, I was just curious if time was an issue.
As I'd said I haven't done this in a while and the last time I did it was at the graveyard and the wrong ghost ate my Ambrosia. It was kinda funny! IDK who he was, but he was really happy and took off to wherever! That was long before mods though.
This sim isn't really all that important, I was just kinda like, "oh darn, their sister died...when the heck did that happen?...hey I have a deathfish just chillin in my fridge with some life fruit...let's bring her back!" I will give it a week or so, then just stick her back in the graveyard if she wont eat the stuff.

I do think it's kind of crappy that EA hasn't bothered to give the mourning icon to family outside the active lot when a family member passes. I'm finding this to be an issue now that my families have all grown so large in all my games and moved into their own homes! What's going to happen when the parents/grandparents die and all their kids who aren't around wont even show they know? So far the head of each family is still alive and I've been playing them all for a year now, (close to maxed out lifespans for adults and elders) but those original parents will be heading there soon. My first game couple only has 82 more sim-days. Though I know they don't die right away. I think it sucks that no one will mourn them if they aren't on the lot or part of the active family! I'd already planned on just attaching the mourning moodlet to all the family when this occurs. I did this another time for someone I had killed off, but the sim just cries and there's no thought bubble showing why.
On this note: Do any of the mods actually allow for family members to mourn who are not the active family? I held my first funeral for a NA sim friend and that didn't help, I figured it would allow other sims to "know" they'd passed, but nope. The death and mourning really kinda suck in this game, not that I'd want my sim bawling around the game 24/7 but a bit more realism would be nice.
Also, it's kinda dumb that there isn't some kind of system in place that allows mourning and the degree of it based on how close a sim was to the other sims. How silly it's 2 days regardless of who dies. I usually delete that moodlet if my sim sees some random "friend" die at a party or whatever. Unless they actually were close the random crying then jumping for joy bugs the crap outta me. Still for family and friends the sims were supposedly really close to it should be a bit different! I also think it would be nice if, for at least a sim-day, the sims who've lost someone really close would lose the other moodlets that keep them laughing and giggling and such. ie: beautiful vista, attraction nearby, etc. Some kind of bummed out actions would be better.

I guess if you really want to traumatize your sims' grandchildren, you could invite the elder over to die on the home lot. Then everyone would have the appropriate moodlet. (I always get an alert in my game when someone my sims know but who lives elsewhere is about to die—the game rolls the outcome just after midnight, and the "call" comes in a few minutes later.) And even if the whole family has a pile of positive moodlets, the combined -100 or whatever it is for "witnessed death" and "heartbroken" can put a damper on anyone's day.

By the way, I usually play on normal lifespan, so a two-day moodlet is equivalent to two years of the sims' lives. I think that's more than enough mourning for them.

Also, I know it's not important right now, but I've developed a bad habit of cheat-console resetting graveyard ghosts who start annoying my sims. It's usually when they're fishing for deathfish—the passing ghost distracts them, and I have to start over. But the same principle could apply to one of them going for the ambrosia. Or you could wait until your preferred ghost appears and then take your chances.

@JohnL83: Twallan added the following option in Story Progression to fix this issue many years ago.

Propagate Mourn Moodlet on Death
When enabled, the mourn moodlet is propagated to all closely related relatives
Default: True
Module: Extra StoryProgression

Thanks Sarah_Sims, I had not seen that and I have SP, does it require any of the extra SP options? I have SP Career extra and I'm not sure about what others, if any I have downloaded.
Puzzlezaddict - haha traumatize the kids? ...No I get what you're saying, but I still want it to seem like the whole family knows someone died. All the "children" of my sims who are out of the house are adults now with kids and only a few still in the YA stage. The only ones that are teens or younger are the grandkids and in a few cases great-grandkids. So just a mourning moodlet to anyone connected by blood or close relationship would seem more realistic. (thanks again Sarah for pointing out something I'd missed)
I built a system in my game that I'd read about somewhere so that a sim year balances out to real-life type life spans, adult and elder are the longest, cuz if you think about it you don't even retire until age 65-70 and I feel like YA really ends around age 30 so there's a whole other 40 years before you're considered "old". (by realistic standards, not by a teenager's limited point of view.)
What I get annoyed by is that all my sims seem to jump for joy and laugh immediately after the crying for a few seconds and it just so strange and disconcerting to me. It seems like being more bummed out that mom, dad or your spouse passed away would be a bit more tactful. Nothing annoying mind you, the out-loud crying annoys me too. LOL but maybe a moping around sim moodlet for a day at least? When my dad died I was 26 and I didn't feel like jumping for joy for a while, even though the family and I had some laughs about Dad's quirks and the good times we'd had. But that's not quite the same thing. I know, I'm asking for too much with sims who "feel" nothing really...just sayin...
Oh yes and the ghosts bugging my sims is a peeve of mine too, we don't visit the graveyard much anymore, I built a personal plot on land nearby for my sims and their family and close friends to RIP. I also created an extra fishing hole in a couple of my towns where you can get deathfish so we can avoid the graveyard.

You're welcome John!
You need to have Story Progression's Extra module installed for the option to show up, as stated by the words Module: Extra Storyprogression in my previous post.
It's enabled by default (Default: True).

Well thank you everyone, but guess what? Patience was the virtue here because the when I loaded the game today and night fell, the fist thing she did was eat the ambrosia. Then ran home to join her family staring at the walls in the foyer and no one even bothered to welcome her back. LOL
Not that I was expecting that, we all know the NA sim secrets. Sorry for the lengthy reading required here which in the end was for nothing, okay, not really, I did learn some things so it was good info.