Is this girl assuming that I have no friends or something...?

[Woofy]

If you want to keep this friendship at any level, you probably should have a talk with her, and ask her, straight out, friendly though. 'I know I seem to be available to you and like I have no other life, but i guess you may as well know, I have friends, dance friends and such, and you don't have to feel sorry for me. Why do you do that? Put her on the spot. She cuts you off, she doesn't see you.
Make sure it's just you and her, and then she will look around in the future and notice that you are not a shallow block of wood that drops out of the sky available to her whims and her using you.
By the way being offended, is anger,; and it will be all gone once you deal with what ails you as soon as you can because it festers and erupts later, guaranteed.