I think adjusting expectations seems sensible rather than abandoning the friendship.

Sometimes we just have to accept we aren't going to change people and they likely won't change themselves either. Sounds like your friend has coped with quite a lot recently (loss of parent, marriage problems) and your description of how she has lost her spark is sad, she must be aware of this on some level even if she does not admit it and is projecting how she feels onto others.

I respect your loyalty to her and maybe things will settle in the future into a happier friendship again. I hope so!