I'm gonna echo others here and say that she didn't do anything wrong. She came over, you guys decided to have sex, and it was super casual for her. I do understand that you like her so it makes you feel bad that she doesn't reciprocate, but she didn't know that. It sounds like you're making it weird. Don't worry about it so much, there's nothing wrong with casual sex. You can still be friends with her and the group. Or if you don't want to be, alright, then don't.
When my ex of 12 years and I broke up, I was so ready to have casual sex friends... tried to make it happen, I ended up meeting someone I didn't feel casual about pretty quickly before it ever did though, my current girlfriend. I mean it was casual at first but we developed feelings pretty quickly. The idea of cool people who I like to hang out with and sometimes have sex sounds amazing to me. I never got to have that in college either because my ex and I met at the beginning of college. I'm kinda envious of you to be honest.