What do I do? she asked him out but hes my bf!!!!!!?

This new girl at my school named *Rachel* is always is flirting with my bf! they are like best friends and when i told my bf *Danny* that i wanted them to stop flirting so much he said listen *rachel*, we need to be just friends not dating cause i have a gf, (when he said this i was right there) and *rachel* was like who? and he was like my gfs name is *emily* (its funny cause she doesnt know what i look like) and she was like thats too bad shes gonna have to deal with it. and today before school *danny* recieved a txt from *rachel* saying i love you lets go out? and he just sat there staring at it he never txted her back. and today i was going to go up to her and say hey *danny* has a gf so why would you ask him out?? but she wasnt at school. should i say something to her tomorrow about it? but *danny* already told me that he wasnt going to break up with me for *rachel* im so confused HELP?