need some help

ok so a few days ago this girl i know, shes a friend, told me she was gona come to my school on her day off and write on my car. I warned her taht if she did i would ahve to get her back (just kinda joking around i thought). But she did it anyway. So now i have to get her back. Any ideas of what i could do. I dont want to damage her car obviously but just make it annoying for her to clean up. Any ideas? thnx guys. But remember, nothing that leaves permanent damage. Thnx again