Need advice. My fiance has been wrongly reported for "elderly abuse" .?

A sibling did this in an effort to take away her power of attorney and gain access to their Mom's very small estate. My fiance has been caring for her mother who suffers from Alzeimers and has done nothing but care for her and and has made many sacrifices in doing so. She makes sure her mother gets proper meals and medication and has contributed financially to her living expenses and totally dotes on her. There is nothing to hide, but the law requires an investigation of course - rightfully so - elderly abuse does happen. This "report" was filed by the sibling who is about to be evicted from yet another residence and has a criminal record and wants to move in to Mom's house. Questions are - what to expect, what to say or not say when she is questioned by Health and Human Services.