I hear you trying to figure out how to help yourself so you don't keep thinking about these things. You have to "accept" what happened and that it is in the past; that it did not make you good or bad and was not your fault if you were a child. You also, unfortunately, have to take "possession" of it and what it might require from you in the future, not share it with those whose business it is not.

Ignore and/or walk away from your sister if she tries to discuss the subject, just telling her, "this is none of your business and I do not appreciate your continued discussion of my business." If she does the whole, "I'm only trying to help" then give her a cold, "Well, you're not!" and leave her presence. Do you have a therapist/professional you can discuss this with? If your have to go to court, I would get a lawyer/someone to represent you and with whom you can discuss how to proceed. Just baldly state to your sister the "facts". If she is pretending to be a lawyer, remind her she is not either your lawyer (it's not her business) or any sort of lawyer at all so she can go pretend somewhere else.