You need to stay strong, and don’t show her that you are hurting... I went through this with my great grandma, she had dementia, it got worse when she broke her hip though. After she broke her hip, she thought I was a younger version of my mom. It broke my heart, but I had to go along with it, she would always tell me stories about when she was a little girl living in Italy, and when she moved to Baltimore.. even when she punch a boy that she eventually became friends with. Lol she pasted away almost three years ago, I miss her tremendously, and she’s always on my mind. I lost a part of me when she passed, but I know she will always be with me.