Pokemon X keeps crashing at the same spot

I've had this copy of pokemon x for years, got it from my cousin, and it worked fine for a while, but a bit ago, I reset the game and it started crashing at the exact same spot. It will crash whenever I get into a fight with a specific Lass trainer in the Santalune Gym. It is required to fight this trainer so I have no idea what to do. Could anyone help?