I don't get it

This happen a few day's ago. My 13 year old was going out with her boyfriend. I was fine with that. But the problem was . She was wearing tights as pants. I told her to go get a skirt in or a dress. Omg she was telling me all the girl's do it these day's. I really don't get it. I all was wore tights under a dress or skirt. What u guy's think. She did end up putting a skirt on