She could have tactile defensiveness which basically means she is oversensitive to certain touch things. Seams are notorious for causing distress and discomfort in a sensory kid. They do work on tactile defensiveness when a child does occupational therapy which is what the treatment plan for sensory processing disorder usually includes.
Since she is old enough to need a bra then we are not talking about a young child here. They do make seemless bras that she may feel more comfortable in or a sports bra. I would talk to her about modesty and that if she 'needs' a bra, she needs it and it is socially acceptable to wear one.
My son had a great dislike of socks. He resisted them and our rule was that at home he didn't have to wear them. It could be below zero and he'd have bare feet but that was okay because he was in the house and preferred no socks. BUT when he left the house and wore shoes, he had to wear socks. I bough seemless types and if he found a certain brand he liked best---------- that's all he would wear. I catered to his comfort level and bought socks he found most comfortable. Same for t shirts. No tags and they do make them this way now. Underwear----- no tags as well. So, I bought the items based around what made him most comfortable and that seemed to help.
what in the world makes u think she has to wear a bra, THEY ARE UGLY, they stand out like sore thumbs, ACTUALLY 10 X MORE SO.
if she wears loose shirts, leave her alone
when did she start menses
when did she start to develop breasts
I dont think you need to put a label on children for minor things that happen , there is no doubt some children do have disorders but not for this kind of behavior in my opinion.What age is she that a bra has to be worn ?