Ages it should be okay for girls to wear thongs?

yesterday i was in my daughters room and she had thongs in her laundry hamper. when i confronted her about it she said she bought it herself and i shouldnt worry about it. i walk over to her drawer and opened it and find two more thongs. i ask why she had these she said because she is on the dance team and hates when people can see her pantylines through her pants. anyway, i grabbed all the ones i could find and hid them from her. she got pretty pissed at me and has not said a word to be last night or today. was i overreacting? should i give them back? and what age do you thinks its okay for girls to wear thongs? she is 16 and a half and she doesnt have a boyfriend.