Can my sister who is POA for our mother, purchase her condominium? Btw my mother is incapacitated sand resides in a nursing home. We live in PAthank

My mother suffers from Alzheimer's I had been the executor of her will for years. She became delusional accusing me is stealing from her. My sister and aunt took her to the bank in 2014 opened new checking account, made new will and made my sister POA! All of this was done while she was very ill. It's been a horrible situation. Mother was deemed incompetent fall off 2014 all of family stopped talking to me.My sister moved herself into my mother's paid off condo in 2017 maybe late 2016. I found out today my sister purchased the condo in September 2019 for $30,000!!! I'm in shock I didn't think she was able to live there instead of renting it out and making money for my mom and now she buys it for much much less than market value!!!??? I'm beside myself but wanto go about this the correct way. I hope I can nail her ass for this lowdown move she's made. Meanwhile I got sick had a breakdown and lost my home of 30 years all while my sister never owned anything always took easy way out