Looks to me like she has become a free agent of sorts, disassociated from her coffin. The error isn't on Dismiss exactly, it's on what is supposed to happen first after that --
Sims3.Gameplay.Objects.Environment.Sims3.Gameplay.Objects.Environment.BonehildaCoffin:ReturnBonehildaToCoffin

Have you tried MC resetting the entire lot, I think I suggested TAing her prior (this may not be possible as she isn't a real resident sim exactly) or force deleting her and her broken coffin some other way? How about the old fashioned evict in Edit Town, copy lot, bulldoze, replace, and move everyone back in?

Would it be possible to revert to a prior save from before Bonehilda started erroring out like this? Afraid I have nothing else to offer at least until our developer sees this thread, unless other players here have experienced the same sort of thing and found a way through it.