I say "Hi!", she says "Yes!!"...what does she mean???

I would have to know the history of you two be for I could compltly answer this question. how ever she coul be answering you like for example if my brother calls me by name I would say yes. you get what I'm saying?

I answer people qith the word yes no harm is ment by it :D

Or did you ask her out and give her time to think of the answer this may be you asnswer as in Yes! I will go out with you x

she means she wants to know what you want from her. So when you say hi, it's kinda like. yes in a way how can she help you?!. get it?!

Check to see if she does the same thing with other people. Maybe its just her way of saying "whats up"?