Super Clingy Person...?

i know this girl in my grade who talks to me sometimes. i don't really want to talk to her because (i know this is mean) but i don't really like her because i think she is annoying. now she thinks that we are like best friends and that we need to hang out ALL THE TIME. now she has started wearing the same kinds of clothes as me, wearing the same jewelry, doing the same hairdos that i do and even talking the same way. I don't want to make her feel bad but i am SO sick of her trying to be like me all the time. i just want her to be herself but, how do i tell her?