Greedy and selfish sister. Advice?

My sister gets paid as a caregiver from a Medicaid company to care for our grandpa but she does the bare minimum (I'm actually doing most of the work). She is actually scamming Medicaid and exploiting me. My mother (grandpa's Power of Attorney) knows about it and will cover and defend her for it. While my sister is on the clock, she is out working some other job and I am the one filling in for her taking care of grandpa. I cook, clean, make sure grandpa bathes, take him to adult daycare, make sure he is fed, make sure he takes his meds, does his laundry, etc. When my sister comes home from work, all she does is relaxes and does what she wants. She lives with grandpa so she is more like a sitter making sure grandpa is alive and breathing. And Medicaid can only pay for 1 caregiver. I told Medicaid about it to 2 employees and one of them told my mom what I said and mom screamed at me and said "Do you want your sister to go to jail? What do you want?!" I believe the person who is actually working and doing the job should be the one who is getting paid. Not only that, my sister doesn't even contribute financially and she is generating more than 1 income and she doesn't help out. She claims she has no money (since she has debt to pay off so she says) and she doesn't even pay for gas when my parents take her to and from work. She eats the food that I buy and cook and doesn't want to help out with the groceries or share her food or anything else she owns. She is greedy and selfish and hasn't appreciated or expressed her gratitude about anything I've done for her. I can't talk to my parents about this because they side with my sister and they are all negative and verbally abusive people. If I communicate with my sister, she may become vindictive, passive aggressive, and manipulative. I can not say anything positive about my sister. I don't know who to talk to about this. I'm taking care of grandpa because he has dementia and he took care of me when I was young.