My mom is not making the best decisions for my dad. What can I do?

I live 600 miles away from my parents, but am in constant contact with them and the caregivers. My Dad has stage 5 Parkinsons with advanced dementia. He lives in a 24 hour care facility, where he has thrived for almost 2 years. (He wasn't expected to last 2 months when he got there) It was his wish, when the time came, to be placed in an adult foster home vs memory care or other facility. (He was the director of the local Area Agency on Aging before he was diagnosed 20+ years ago, and knew what was out there) My Mom is his POA with me as an alternate. I'm also her POA. Mom lives 5 minutes from my Dad. She is in a wheelchair in an independent living Sr apartment facility, where they provide transportaion. She has now decided that my Dad needs to be moved closer to her and wants to move him to a memory care facility, despite my objections, which are that it would be against his wishes; that now the caregiver to resident ratio is 2 to 5 and in a memory care it would be 1 to 12, not to mention the care he's getting now is amazing. It's a known fact that Parksinson's patients struggle severely with moves like this. He now needs 24 hour care, which is provided by the foster home, and is paid for by his long term care insurance. His disease has progressed substantially in the last few months (he has started to choke more, etc) If she moved him to Memory Care, she would need to hire a 24 hour care giver and pay for that out of pocket, which she can't afford since the LTC is capped. (I manage her and Dad's finances - she's unable to do that - Dad always did it) She's been doing strange things too like bringing my Dad food he would choke on and trying to get him to eat it (he doesn't have teeth) before the caregiver sees. She thinks she can live with him in a 1 bdrm apartment in Memory Care, and take care of him, despite her having severe health problems herself. Last fall she gave her apt 30 day notice and tried to take my Dad out of state before I was finally able to stop her. (She was going to fly my Dad, who can't walk, and has a 24 hour catheter!) My Dad's Dr thinks he should stay put. When I try to convince her that Dad should stay put, she threatens to turn me into Adult Protective Services and won't speak to me for weeks. I feel like I need to protect my Dad from my Mom. I feel helpless. What can I do to stop her from moving my Dad?