"I got laid for the first time last night", would that be OK as a political statement?
I like how you're accusing me of judging when what I'm doing is questioning. Teenagers now have far more sexual stimuli than when I was one, but they seem to have less adult leadership in working out the confusion at that age. At 15, she may or may not have discovered she is a lesbian, and she may change her mind a few times before she's 30. But, I question whether advertising her sexuality of the day is a good thing at that age. Adults question it themselves when there are far more consequences. Maybe there shouldn't be consequences for one's sexuality but when there are it's reasonable to be aware of them.
Maybe she's wearing it in solidarity for some friends or relatives, or political movement. That's easier to deal with, but, again, would an advertisement for a group sex club or prostitution be OK?
The question is whether the message is age-appropriate, not whether you or I agree with it.