How do I get rid of an annoying friend?

Well this girl has started hanging around with me and my friends, and she's really annoying. It sounds so horrible and vain but I'm embarrassed to be seen with her. She's hugely fat, she has a greasy perm, she wears these horrible tracksuits with black pumps which really dint look good together and she acts like a little kid. She has other friends but she's taken a liking to me and my friends. How can we subtly get rid of her? We've already tried avoiding her at break time but she always finds us and we've told her that her other friend was looking for her but she just goes 'oh well!' and follows us around. She doesn't take a hint when we ignore her and she' s just so embarressing and annoying and we can't talk about the stuff that we wanna cos she'll go and snitch it. Ugghh but I feel so mean at the same time! How can I shake her off?