I think you are doing a good thing with what you wrote. From a middle aged women, I must inform you, this stage in life sucks, emotionally and physically. Maybe the way she talks to you is due to this horrible hormonic change, or that combined with some underlaying disorder. I do not have any answer, but it sounds like you are doing a good thing.
If possible, maybe you can encourage her to get some therapy ?
All I know from being a caregiver myself, is that you are doing right things, and don't feel defeated if things reflect from her about her. Just tell yourself you are doing or have done your best.
I wish you lots of love and luck.

DE