Elementary School Kids

I know this is going to sound like a strange question, but is there anything wrong with a developing 12 yr old girl only wearing sports bras? My 11 (soon to be 12) year old SD started developing over a year ago. She's still only an A cup size but refuses to wear regular bras because she says they are uncomfortable and pinch. I can only get her to wear sports bras and for the most part that works out fine because she mostly wears t-shirts, but if she dresses up, the sports bras don't look right. My question is less of an asthetic question but rather I'm curious to know if it will have any adverse affect on her development since sports bras (well at least the ones she wears) don't have much support. They're just lycra and hold everything in rather than support anything. Is there a point where she will need to wear a real support type bra or is it fine for her to continue wearing only sports bras even as her cup size grows?