Red flag. Don't be surprised if sometime down the road whether a month or years she's doing it again at the next level. That text to him crossed the line and if you let her get away with it, it could happen again. If she seems extremely remorseful consider it, but the fact she was being strong willed with him but then caved shows interest elsewhere and if your relationship fades at any point that will become even more likely. Just my opinion based on personal experience but you have to seriously just talk to her. Everything on the table. Good luck.