My personal opinion...she could just be uncomfortable with her body and have insecurities. That would explain covering them up. I was always a tomboy and always double layered sport bras. I'm not gay, I'm happily married to a male. I really don't think the abuse would "make" her gay. She may naturally shy away from boys b/c of the abuse, but, that wouldn't make her like girls in a sexual way. You said she was a very young child...how young?? Does she even remember the abuse? If you're worried about the abuse affecting her, I would suggest she get into some counseling. Being a survivor of abuse, it would have made a huge difference in my life had I gone to counseling at a younger age.
I substitute teach at a large high school. It seems like half the girls there wear nothing but jeans and a sweatshirt everyday. It may just be the clothing style for now. I also kinda wonder how you know that the girls she hangs around with are gay? And even if they are - so what?
I see this time and time again. Many, many people who say their gay have been molested or sexually abused somehow in their past. I think there's a strong connection. If you're interested I can give you the name of a book of a young lady who had this happen to her and her journey into the homosexual lifestyle for many years before coming out and realizing she really was not gay. I personally know of another person who had the same experience and I've read a lot and seen a lot that seems to suggest that past sexual abuse has a lot to do with gender confusion and their sexual identity.