maybe, if you really don't want a gift from her--tell her beforehand? maybe not in a rude manner but maybe something like "this year i do not want to celebrate my birthday in any shape or form, so if people are thinking of getting me presents, please do not"
if she does end up buying you something--just accept it. it does not mean she's making up for not being nice to you the other 364 days of the year OR that you owe her any goodness back.
If you don't want anything from her, pull her aside and talk to her privately. She may truly believe you're a friend in some weird, twisted way.
However, I think that would possibly make an already awkward and hard situation even worse. I'd suggest accepting it with a simple "thank you" and moving on...like the poster above said, a gift doesn't make up for a year of crap, and you don't have to become her best buddy...