So, I was the younger sibling. Some of what you described, my brother did to me. I always understood, that he was abusing me because of the abuse/etc we lived with. He did apologize to me once. He might have even be sober, after all this time, I don't remember. I do remember the apology was sincere, and it mattered.
i think if you want to apologize, and you are concerned you might trigger her, you could write it out. What you've written here is a good start. Even if you don't share it, it could be therapeutic to you. If you do share it, you can let her know that you have written an apology about your past relationship and she can read it or not. I think that's a key part of it. You can't control or dictate her response.
With my brother, I don't hate him and have forgiven him for what he did when we were kids. Having said that, I have cut contact with him, because his expecations for me and our relationship are not healthy for me. For example, in our adult relationship, I heard over and over, that I was selfish because I didn't maintain enough contact for him.
I feel like killing myself will do her a favor as her previous abuser would be gone forever.
No. That's not how that works. All that would do is leave her with more complex feelings to process. Instead of bring resolution it would mean that some things could never be resolved.
. The guilt eats at me every day and I am unsure how long I can live like this
I'm not saying that you should have no guilt, but I am wondering if there are other things underlying this guilt?