First, I do think the WTS involves itself too much in people's choices.
But, I do realize that elsewhere in the community at large, official and unofficial dress codes exist.
Some schools require uniforms.
Some employers require uniforms (and not just the military).
Some employers require more formal dress for both men and women (orchestras, i.e.)
Some employers require employees to wear suits and/or skirts when dealing with clients.
I had a teacher who would have a job interview dress day. He would tell us what day and we all had to come as we would if we were going on an interview that day. Then he would critique us and help us find clothing that was appropriate to keep in our wardrobe. He did that because we spent so much time in casual clothing at school and outside school that many of us didn't even own proper clothing for an interview for the jobs we wanted.
So I think if she is a minor at home and the parent is reasonable about her choices, she could find something that she feels comfortable in.
I no longer attend meetings but still wear skirt/dress for job interviews, weddings, more formal entertainment events such as classical concert openings, fancy restaurants, special events such as anniversaries. I have worked in the legal setting for many years and the judges, lawyers, etc., wear more formal clothing when appearing in court and on the other days, jeans. BTW, the men have no restrictions re beards.
She could consider it practice and preparation for the day she goes on interviews for those serious jobs she wants.
Blondie (culled her closet but still has a few "skirts" around)