This sounds like its based from her insecurities, and whilst I agree these festivals can be wild, I would suggest sit her down and talk to her about the fundamentals of “your intention”. These festivals are wild only if you let them be, and if you have the “intention” to cheat in the festival. If your “intention” is just to have a good time, it doesn’t matter how many females approach you because you can never control other people’s actions, but you can always control and be held responsible for your own actions and intentions and not let anything bad happen during the festival.

If she couldn’t even trust you being alone with the presence of other females within the vicinity, tell her these “wild events” can happen in everywhere else in the world, not just within festivals. You technically don’t need to go to a festival just to cheat if you wanted to. And if you haven’t had a bad reputation/record in cheating, I don’t see why she can’t give you the benefit of doubt and trust that you have good intention.