Small school, its awkward to not facebook-befriend someone. But her wall posts are hidden from my home screen.
Just remove her. Problem solved. Even if it's a small school, 4 months from now you wont be seeing her in person anyway. If she asks, "Im trying to use facebook less, it's addicting." If she gets angry, tell her to hop off your nuts and move on, there's other **** in life to worry about, and walk off like a badass. I swear to god i said that and it worked, in a sorta similar situation (ugly, not fat girl).