Speak to an attorney familiar with defamation and have them send a cease and desist letter, best of luck.
The above answer is for information only; and does NOT constitute legal advice. This answer does not constitute, nor does it create, an attorney-client relationship between KaplunMarx, PLLC, Jonathan D. Marx and any receiver. The information provided on these pages is general only, and you should not act upon this information without consulting with a qualified attorney
If your sister is actually defaming you (as that term is defined in the law), then yes, there are ways to make her stop.
A lawyer can help you to obtain a temporary restraining order and/or a permanent injunction preventing your sister from further defaming you in the future.
But again, this entirely depends on whether her cations constitute defamation under the law. Do a google search for libel and slander laws in your state and ask yourself whether her cations qualify as one or the other. If so, call a lawyer.