My aunt with advanced Parkinson's can't remember to take her diaper off AFTER she gets into her bathroom. What can we do/

Parkinson's is often accompanied by dementia (two common types are Lewy body and Alzheimer's). The fact that she doesn't understand and cannot explain why she does this or even why it's not okay suggests that she truly doesn't understand what people are talking about. Her short-term memory and/or her understanding of issues has been damaged. In this case, she's simply telling you her own truth.

This is tough for caregivers but no one's fault.
Likely the only true answer is to have her in an environment where she can be accompanied to the bathroom.
Take care,
Carol

Thank you, Carol. My take on this is that my cousin has worked so hard to first care for her mother in her mother's own home, and then supervise the care in the facility, that she may have lost sight of how bad it really is now for her mom. And the fact that her mother still has some ability to behave appropriately and has her sense of humor, clouds the fact that her dementia is quite bad now. Stepped up care does make sense, although my aunt really has gotten used to her room and her neighbors on her hall, and her pals at meals. So, maybe the staff can start coming in every few hours and take her to the bathroom, even if she says she doesn't need to go. That might buy a little time before a big change is unavoidable.