Stay on her good side. It's very likely that you'll not see that money again - so I would say - hope for the best, prepare for the worst. If you plan on ever taking her to court - write down the important information now (date you borrowed the money, how much, when you were told she would pay you back, any payments you've received), while it's still fresh in your head. Good Luck :)

Wait until she has a new boyfriend who will loan her the money to pay you back.

Or, if you have some kind of proof of the agreement, take her to court.

If you can prove that it was a loan, take her to small claims court. If you can't, learn from your mistake and never loan someone money (including a girlfriend) without having them sign a repayment agreement.

Sounds like you're in the same position as her old ex. What a bia bia

Have her next boyfriend lend her money to pay you back

Hopefully you have learned a lesson here. Go to small claims court in your jurisdiction. Legal representation is not necessary, but of course you can hire an attorney.