Hi CI
What a terrible story.
Neither of my children have been abused, as far as I know (they are 3 and 6) but I had a traumatic background with abuse here and there, so I don't trust any man, except their father (otherwise I would not live with him) absolutely.
The biggest part of the abuse (mine did not result in long term physical scars) is the betrayal of trust on the part of the adult. You have already gone a long way towards remedying that betrayal by believing her and doing something about it. I don't know how long it will take to heal, but you are doing what you can.
Innocence lost is a great shame at such a young age and it should not happen. My daughters' innocence is more precious than anything. All I can say is that, once having lost my innocence, I became smart enough to look after myself in early adulthood - something we'll all have to teach our teenagers. And, having been with my present partner and the father of my children for nearly ten years, I trust him absolutely, so all is not lost.