YA novel for mature teens (dark tone and themes) about teen girl who takes care of unicorn in her barn/shed

Long (maybe 300 pages) YA paperback novel from the 80s or early 90s (I read it in the early 90s) for mature teens, with a dark tone, about teen girl who finds a unicorn and hides it in her barn or shed to take care of it. I think there is a scene where a neighbor teen boy almost rapes her in the barn/shed but the unicorn intervenes. The book didn’t have much fantasy or magic despite having a unicorn. I’ve been trying to remember what this book was for so long!!!!