At what age do you start to realize you may be a ?

I like to empower myself with knowledge, whenever possible, before speaking to my children about a subject. My 13 year old daughter has been overheard saying she was a . When I questioned her, she denied it and said a few of her friends are and she never said that. I am an open minded mother, who is very supportive as long as my children won't be hurt. If this is something she genuinely feels, then I need to figure out how that talk needs to be handled in order to be productive. Any knowledgeable opinion is appreciated.