I started talking to this girl in a sorority trying to set up a mixer for my fraternity. She's pretty cute. Anyway we start texting recently and I just asked her to grab coffee with me once classes start again next week. She tells me it sounds good then says what is in the title. She has a boyfriend. I really have no idea what to say to this besides "its just coffee so we can talk about the mixer and other things". The fact that I want to have a mixer with her sorority stops me from really wanting to try anything on her. I would really appreciate your advice here seddit. To be more specific, what should I do in the future if a single girl says this to me?

Edit: just thought of this, I could also exagerrate and say something about having flowers ready for her.