Sorry to hear she is doing this. I would suggest not engaging in a battle of words with her. That will just make matters worse and not fix a things. She is going to be who she is going to be. I would guess most family members see right through her; generally this kind of behavior doesn't come out of the blue and family is well aware of the reality versus the stories that get told. She's bitter about losing her life and having to go into assisted living; that isn't an unusual response. She's spewing her anger and her venom and unfortunately it's landing on you. I suspect she'll mellow in time and this will pass, but if you feed it by responding in the same way, it will just exacerbate the problem. Tough position to be in. Block her on Facebook so you don't have to see her posts and she can't see yours. No reason to engage her behavior.