Friend flirting with bf

So I have this softball teammate/friend and she met my bf the other day. She asked for his number and I gave it to her because I don't want to be the girl who's jealous of every other girl in my bfs life. Then she started flirting with him(which I kinda expected but I didn't want to not give it a chance). She calls him hit and cute and has outright told him she has a crush on him. The other day she sent him a photo of her with MAJOR CLEAVAGE with absolutely no reason to (he showed me the convo). She tells me that she feels like his back up bitch. I've kinda made my peace with it cuz I trust him but it's getting on my nerves that one of my "friends" would do that to me. And I just don't know what to say to her or what to do about it. For now I'm just letting it be but some advice would be great. Thanks.