I have three DD's, my youngest is 16.
It was around this age that they started to make the transition to being young women.
They all seemed to start to experience nipple pain and/or tingling, so wore a crop type top with slight support.
There can be big difference in a girls chest and a boys, even if no development has started.
It looked better under the school summer dresses.
OP I think that this is something to consider for when she goes back to school in September.
Whilst I agree with keeping children age appropriate, it us important that girls accept the changes to their bodies, without feeling any shame.
Being allowed to make non damaging personal choices, does a lot for self esteem.
You do see girls in the last year of Primary that need a Bra and I am now glad that teaching staff will speak up about this.
I also think it's important not to link underwear or personal grooming to sexuality, they are seperate, both are biological and not linked to Morality.