This was one of those things that popped into my head earlier today, and I keep flashing back to it. I read this as a library book when I was in Ashland, KY, probably around the mid-90s. I think it was a paperback whose cover was primarily blue, with the girl depicted on the front, staring off to one side. I don't think the book was long, maybe under a hundred pages, and was in English. Early in the book, four boys (I think members of one of the sports teams?) corner her in a deserted part of school, maybe under construction, and sexually assault her. It's not described in detail, but rather as a series of somewhat disconnected moments, I think from the perspective of the protagonist, who is one of the boys assaulting her. I don't remember if they get caught and punished for it, but one of them is consumed with guilt over it, and befriends the girl in his attempt to come to grips with having done it. As I remember it, the assault was not premeditated, but more of a matter of them coming upon her in the deserted section of the school, and what starts out as teasing escalates.
The girl might have been named "Wendy", because I have this vague memory of conflating the character with the title character of the song by The Association. She was Caucasian, and had long hair. I think the boys were also Caucasian, I think.