Target, primark, shien is nice from time to time, and h&m are my top favorites to find for my girls
Online! Lol So many options at your disposal and you can take your time picking stuff out. Just make sure you know her sizes and check size charts. My daughter is 11 and the style you described sounds a lot like the style she is into which is trending Look up cute y2k or core style clothes for preteens girls on Amazon. My daughter just had her bday and I got all her clothes she wanted on Amazon and it looks so cute on her and got a lot of compliments!
Kohls, JC penny, old navy and target is where I go for my SD. Or i go to the mall and whatever i see i go into the store. The first 2 always has good selections in those sizes on clearance if there a bit expensive.