Why does this girl I hooked up with act like I don’t exist when I run into her?

I was in a bar and we started talking and she invited me to her dorm we started kissing then we went to my place. She seemed shy and we just cuddled but didn’t have sex. After a while she asked me to have sex with her. I did. She act normal with me and said she liked it. I see her every now and then on campus most recently today and she acts like she doesn’t know me. I say high and she ignores more or runs away? Why is she doing this?
Why does this girl I hooked up with act like I don’t exist when I run into her?
Post Opinion