my sister in law has POA she bought house at extremely discounted price when she found out mom left it to brother in will. plz help

my mom has dementia, my sister has poa since 2008 my mom had forgotten she had it. anyway my sister 0found out mom left the catskill house to me and she lost it. she said mom needs money so im gonna buy house i said no we can do reverse mortgage on the bronx house a month later she tells me we just closed on the house. i bought it for 200k the house in the worst cond. is worth 243k not to mention she got everything in it including tractors and heavy machinery and all the furniture its a 5br house 33 acres w/a huge barn and pond. she put the 200k in her bank but i see 12k is already gone my mother gets 400 a week my dads retirement and ss and i give rent both houses are paid for outright. she also just paid taxes on that house can she do that? she didnt want me to get the house so her and her husband bought it b4 mom passed. it seems wrong somehow. plz help ps i am an adult disabled child who has lived in the bronx house for over 20 years w/my wife in the apt. down stairs.