Does she need to change her behavior?

My 12 year old niece is acting very mature. She is a very nice girl she plays many sports and gets straight A's and goes to church very Sunday and youth groups on Wednesdays. But she is acting like a 16 year old. She wear high end makeup only wears brand name clothes she has a certain group of friends and a boyfriend. She wears high heels and dresses on certain occasions. She also cares very much about her looks she has her room re done every year. She has a brand new iPhone 5c an iPod and an iPad, TV in her room also. She frequents the mall she is obsessed with American eagle, Aeropostale, Abrecomie and Fitch, Hollister, and forever 21. She also has a coach purse and wallet and a Louie Vuitton purse. Is she acting too mature? Does she need to change her behavior?

She isn't acting too mature, it's just a phase girls go through. Once she turns about 14, it'll go away.

I think she's acting too mature, but she's not the one who needs to change her behaviour.

What are her parents thinking? Why are they pandering to this behavior? Why are they wasting so much money on ridiculous things? All they doing is creating a horrid spoiled brat!

No, her behavior is fine.

Girls mature quickly, and they also mature faster than boys, so in a few years, as someone else said, the phase will go away.