Put her hair in a ponytail? She'd rather stick a hot poker in her eye. My 7-year-old daughter Campbell is a tomboy through and through.
She stopped wearing dresses when she was two. She won't even wear a tunic because it too closely resembles a dress. She's VERY proud of her tomboy status. I too was a tomboy. I tell her it's OK to be both girly and be a tomboy. She doesn't buy it though.
I didn't think it would ever happen, but we had a breakthrough. We were at the beach and I suggested Cam put her hair in a ponytail so it would stay out of her face. And to my shock, she agreed!! I quickly put up her hair before she changed her mind. She looked so different. My husband and I instantly followed with compliments galore. You know, that powerful, positive reinforcement thing.
I said "Wow, Cam, you look older!" And that did it. That pushed some kinda button with her. She perked up and said, "How old?" And that was all she wrote.
The next day she was playing around with her hair and held it up on top of her head. I put in a clip to hold it in place so she could get a look. I told her how cute she looked. She was LOVING it! I've never seen her respond like that. She wore her hair up every day AND she wore a bikini, which she had also refused to do.