I can relate to a lot of your story. I have a sister who I've had a dreadful relationship with for a long time and the backstory also involves sexual abuse that was minimised. Our difficult childhood has messed up a whole lot of things and made for a very fractured and dysfunctional family even now.
However, I also think the abuse can also act as a red herring in that it can be seen that something that we both went through and that knowing how it was binds us together. I actually resent that because I think I'm a very, very different person from my sister in a lot of ways, and part of my problem arises from her thinking we were really close, and me really not liking her but having to suppress it. A history of abuse may explain some things, but it doesn't mean you're obliged to forgive everything or put up with any old kind of treatment IYSWIM.
I haven't taken quite the same route as you as I tolerated a lot of controlling and needy behaviour from my sister up until a few years ago, when having my own children made me really put my foot down with certain family members. I decided to put my own DC first and stop treading on eggshells around my sister and having all my energy drained by her. Of course it didn't go down well at all and now we barely speak, which suits me fine in itself but I also feel guilty and sorry for her.
So it's kind of the other way round. But I would say you showed a lot of strength and self-preservation by standing up to your sister when you did, at such a young age - I wish I had been able to do that. You're now in the position of having her want to make it up, but you hold the cards. I think that means you can (if you want to) welcome her very cautiously, take it very slowly and if there's any sign of her not treating you with respect or being overly needy, you can back off and/or explain that you aren't up for any of that.
One thing that concerns me is that your sister seems to need your parents - but she was OK when she had a man - and now she's approaching you. It suggests she leans very heavily on whoever is closest to help prop her up. You don't want to end up with an unbearable level of responsibility for her emotionally, and that's why I would tread carefully.