So my [M] girlfriend [F] made a new friend…

So my girlfriend is bisexual, I am straight. She has a female friend who obviously has a crush on her. And slowly but surely it’s been slowly getting a little bit more flirty and this friend eventually sent sexy pictures saying stuff like, how do you think this bra looks on me? A few weeks later we got pretty drunk and we were talking about it and I asked what she thought about it and she admitted she thought it was hot and I asked if she would ever send something like that to her. I know she had never been able to express her attraction towards girls as she is only 18. She said she would but it would feel embarrassing, I said why not try it and see how you feel.