What do you do when your Mother has appointed someone else as POA just recently and didn't tell anyone.

My 75 yo Mother has Severe Lewey Body Dementia.She appointed me as her POA 2 years ago. Now the Neurologist 4 months ago told my mom that she would not do any treatment until she got into an assisted living site to monitor her meds and rehab. So we waited for her to do something like she said she would. Nothing. So I started looking and found a great place. She and I took a tour. And my family told me to put a deposit down on a beautiful studio for her. She had an evaluation and was approved. NOW she tells the nursing staff there that I am no longer her POA.I don't know what happen except I think she really thinks that she will be able to make the decision. Which she can't, it is getting really late and she is getting worse weekly! NO ONE KNOWS WHO THIS PERSON IS!!!!!
She refuses to acknowledge the problem and says she is fine. She also told the home staff at the interview that the doctor has not told her she needs a home or any assistance medically. That she would make the decision and no one else. The problem is that the lawyer did not know about the disease, and had her sign the new papers. She is supposed to move next weekend into this beautiful place. NOW what do I do?!!??!! Do I need to have the Doctor write a letter concerning the issue for the lawyer? Do I just let her leave and let her be with this new POA and let them deal with it? IS the new POA document legal? I am at my wits end.