Jealous siblings are really hard to take. She sounds a lot like mine...I have dealt with her by deciding to limit my exposure to her.
Don't agree to babysit, don't go round there, don't invite her over.
Tell your family not to tell you the stuff she says about you, just do not discuss her.
Do not engage in conversations with her at family events, just be very , very boring, don't say much other than mmmm, and avoid her if possible, go freshen your drink, or go to the restroom . Don't give her any information that can be used against you.
This is very hard to do, but since deciding to limit my contact with my jealous sibling , I feel so much better!
We can't choose our family, but we can choose how much we interact with them. Choose to surround yourself with positive , uplifting people.