I'd say yes you're a friend to her along with her other friends. Usually asking a girl to homecoming means you escort her there and it's understood she's with you. This is not what's happening in this situation.
I would ask her outright if she considers she's your date or if you're just hanging out as friends because if she's not your date then say you'd like to ask someone else. If she says she's not your date then feel free to ask someone else and who knows when she sees you're not just waiting for her you may become more attractive to her.
Don't let her use you as a doormat.