Sports bras are cool beans; often I wear one and so does my young daughter. Sports bras are nice and comfy. Except your mum had no right calling you hurtful words. You have a right to be treated with respect and kindness and I think you should tell her.

Asserting ourselves doesn't mean loud. Lower your voice, keep eye contact and ask her to be more mindful of your feelings. You're adult now, remind her, so she has no right to treat you like a child.