It would probably depend on what she did and how she did it. If she was straightforward and honest about it, probably nothing. But consider the gold-digging ex from several years ago who decided it would be a good idea to cheat on me with my best friend at the time, was incredibly shady about it, and denied it once I found out. Her, I got fired from her job. Him, not a thing, because if a man steals your wife/girlfriend, there is no better revenge than to let him keep her. I did go see his parents and let them know what was going on - they own a bank and have considerable assets to protect. They disowned him and wrote him out of the will. Pictures on the web are amateurish.
wow
i have been tempted to do this in the past but i realized it doenst change anything. its not going to cause them to get back with you nor will it ultimately make you feel any better. i think after some time you might look back and think, man i was a jerk haha. it might make you feel good initially but if you really want to stick it to her move on with your life and show her that you are 100% ok and maybe even better off without her.
this is kind of what happened with my now fiancé. she went bonkers and wanted to break up so i let her and two months later she came running back to me because i showed her that i had my own life. now we're getting married. relationships are crazy. in my experience do what ever you feel is the opposite of right is hahaha.