Well this works better with guys with gay porn but i bet it will get more or less the same effect with girls.
Step 1. Go to your local book store where ever that sells porn, hope you dont see anyone you know and buy lets say 5 gay porn mags (in your case probably just straight up porn)
Step 2, cut out as many individual goodie picturs as possible
Step 3, put them everywhere, in their socks, randomly in books so when they go to class and open a book BAM COCK IN YOUR FACE! in drawers, shoes, car, anywhere you can think of. even when she thinks it is over, she will find more.
I found this one somewhere on here once and i never had to use it, so not my idea but could be worth a good laugh if she didnt piss you off that bad