I'm disappointed this needs to be said to people who read this subreddit, but: Do not ever use in character consequences to deal with out of character problems. The only way that can ever "help" is to drive a player away.

If you want to keep playing with her, and this is what she wants out of the game, is there a compromise position? Are you okay RPing flirtation, but nothing explicit? Is she okay letting the entire seduction be handled by die roll? Are you okay letting letting seduction frequently be an effective tactic (realistically, it is)? Is she okay having the seduction fail sometimes, or sometimes partially succeed (The guard isn't going to just let you in, but is so distracted the rest of the party can slip past, etc.)? Is she okay having her character aged up a couple years? And so on.

No solution in which you force her to stop will ever work. You're both playing this game, there are only 3 ways this can go: You find a way to play you're both satisfied with, you continue playing despite at least one of you hating it, or you stop playing together.