Wait... she made out with another girl while playing spin-the-bottle drunk?
That's not cheating... that's fuckng hot. See if you can get her to do again when you're around. There is no reason for either of you to be upset... spin-the-bottle never counts as cheating. Okay, unless you fuck someone else but those aren't the rules of spin-the-bottle. You two are young... have fun... make out with people...
Maybe you need to make out with a guy now.