How do I dispute a fraudulent POA filed by my sister?

Question Details: I was named POA and appointed Trustee of my mother's estate 9 years ago. The doctors deemed her mentally incapacitated and I have 3 doctor's letters to confirm. I've been living with and caring for mom since. My sister who has a colorful past and an active restraining order, took my mother from our home when I wasn't there. She coerced mom to sign a cookie-cutter online POA appointing her. My sister then presented her "POA" to banks, renters and insurance companies. She's been intercepting rental income and accounts have been frozen making it impossible to maintain financial integrity of the Trust. My mom hasn't had capacity for the past 9 years so my sister's POA is illegal. What legal approach can I take without significant financial impact to my mom's estate?

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