In PA the existing Executor of the will, POA, has to sign off on the new will. Does that still apply now that mom is in NY?

My sister had my mother change her will, POA and Executor, to her after my mother moved in with her without my knowledge. The will was written in Pennsylvania. After my father passed 10 years ago, my mother moved to New York and alternated living with my sister and me. She developed dementia over the years. She is now 87. She went to visit my sister last Christmas (who hasn't spoken to me in over 30 years because she thinks I received more than her and was the "chosen one".) We had the same opportunities in life. It's what you make of it. She is 68 now with no income except her husbands retirement, which isn't much. She had my mother sign over POA and assigned her to be Executor of her will. My mother has no clue why she actually did this, besides to say it's what she wanted to do. My sister has closed my mother's checking account. I have no idea where my father's retirement now goes or what she does with it. I have not seen my mother since she left. I call several times/week and no one returns my calls. My mother's cell phone has been taken away from her, so I have to leave a message on my sister's answering machine. No one has spoken to my mother in 1 1/2 years except for her one sister who refuses to tell me anything. She says she wants to stay out of any family business. My mother writes an occasional letter and says she's very happy there and will not move again. One question that I have, among many others, is, was it legal to change my father's and mother's joint will (written in Pennsylvania and now changed in NY). I know in Pennsylvania the existing Executor of the will, POA, has to sign off on the new will. Does that still apply now that she is in NY? I am desperate to get my mother back safe and sound. Now knowing what is going on with her is the worst part.