What to do if my sister had a will made up 3 years after my parents original will, making her POA? Signing docs for them?

My parents had a will drawn up in 2005, making my brother POA, he passed, making me POA, then my youngest sister. In 2008 she had an eldercare attorney draw up new papers making her POA. Since then, she moved all their money, $300,000.00 into her accounts, sold many of my parents items, collected money for their care, which I have been here with my mother 24/7 since her fall in 2014. My mother at the time had severe delirium, d/t a thyroid storm, and my father was dx with dementia.
Now that the money is gone, and she collects for her care, which she may show up once a week if I'm lucky, has given me orders to pay the bills!!!
I don't know what to do! I am mainly sad mother who was so good to everyone, has to end her life like this.....it is just killing me. I don't mind taking care of her at all, like many others, just fear for the future, and want her to be happy....:'(