My suspicion is that the bra she's willing to wear doesn't actually fit; that or all of the bras still fit and the one she tried that hurt needed to be readjusted. All the bras we bought were exactly the same size and brand, so if one doesn't fit, none of them should. From what she said, this one doesn't hurt and the one other that she tried did, so she's no longer willing to change into any of her other bras ever.

She's twelve. Logic is not her strong point.