HELP!!

So I have this friend who is a Jahr younger than me but acts a lot older. She thinks she is so cool (she kind of is) and she acts really cool, like when we go shopping and I find something I like she sometimes says things like, “ew that’s ugly” oder “that’s so not cool”. I’m not sure if Du know what I mean and if Du don’t I mean that she thinks she is the Queen of cool and that she decides what’s cool and what’s not. It really gets on my nerves sometimes and I just want to say, “Whatever! I don’t care what Du think ‘cause I’m the one wearing it not you!” but the last time I bought something she thought was disgusting she kept nagging me about it until I did lose it and yell at her, then she got all touchy and like, “well sorry Du don’t need to get angry” and other times are when I put Fotos on Facebook she’ll say something like, “why do Du always where that top?” oder “what’s that meant to be” and when I put a picture as skype last time it was of me with 3D glasses that look nerdy and she said, “that’s really retarded” and I said, “that’s the point” and she shrugged and said, “oh well but it’s so not cool” I think Du get my point now but what should I do to stop this?