S.H.
What I found, is that it is important for a child to have a sense of their own "identity" and uniqueness. Be that from their interests or the activities they participate in, and how they are at home.
My Dad and Mom raised me and my sister that way. Basically reinforcing OUR own ways of being... and not trying to be like everyone else, and teaching us about character. And they showed appreciation for our own unique characters. Therefore, we didn't try and just blindly follow others that were not good influences.
For me and my Hubby... from the time my daughter was very young, we always emphasized that she just be herself... not having to be like what she saw on TV or like other kids. BUT THE KEY thing as well... is that we taught her how to DISCERN between what is positive and what is not. That just because some other girls may dress a certain way or act a certain way, does NOT mean she has to too. My girl is only 6 years old, but she has such a sense of herself already...her own identity, and she does not try to copy-cat other girls that are more precocious or 'sassy' or more over the top. And, we let her explain to us how she feels. She is ABLE now, to judge others on her own, and "knows" instinctively who is not a good influence. And more importantly, she is 'proud' of herself no matter what.
The "American Girl" books are a good series. It deals with ALL kinds of topics of this age set. You can find it at any bookstore, or at www.amazon.com and you can read the reviews there. I even got some for my daughter.
And like anything else, they need to feel a real sense of identity. So that they then don't go and seek approval from outside influences that may be bad. AND, knowing HOW to analyze situations and people. Then, they can make the right decisions... and how it will impact them. Mostly, my own Parents taught us that by actually discussing everything with us... my late Dad for example, would even take us to his business meetings and let us sit and observe and he would 'explain' to us his own thinking and why he did certain things... and how HE decides who to be friends with or not, or who to do business with or not. Children... need to learn how to make decisions. BUT, it is taught to them... it is not always instinctual. So, they need to be shown how to make decisions.
Just try and keep open communication with her, especially at this age, it is VERY important. No matter what, for bad or good things... let her be and talk with you about anything. A child needs a 'rudder' to guide them, or their ship will just have no course to follow. And this rudder is the Parents and the child's own home. It's their 'base.'
Or as others said, have her get involved in a club or activity that interests her... something she can learn about.. something that she yearns for....something that she perhaps has a talent for... these all provides a positive thing for a pre-teen. It's good her school has a program to help kids.
All the best, just some thoughts,
Susan