Hate to hear the bad news man. As stated, don't take her back although you'll want to. If you do she'll know she can get away with it.
Good payback options would be, sleep with one of her friends, tell her mother what she's done, put a wedding announcement in the paper in a week or two with your most attractive female friend, rub one off on her luffa(sp), or you could claim you only dated her to hook up with her prettiest gf
It'll work out