My sister is suing me for my house plus additional money

my mother had a massive stroke in Nov. 2018. She bought a house for me (her son) and my husband because she was living next door to us and we cared for her for 2 and a half years, before she died Oct 2021. My sister was notified Oct 2019 of this and tried everything she could for my mother to change her trust before she died. Now she is coming at me for my house, plus $425,000 saying my mother was not in her correct state of mind when she bought us the house. (she has a bogus P.O.A. since jan 2019, that she has used until July 2021, even though a lawyer told her her P.O.A. was no good, EVEN IF IT WERE REAL, because my mother had signed a P.O.A. to me in Jan 2021. ) She never acted on anything regards to my house till now, after my mother passing but wants all money accounted for since my mother signed me as P.O.A. My mother was never seen by a judge or a doctor saying she was not able to take care of her money, and I just did what my mother asked of me.