"For the girls" labels something as enjoyable mainly by women and queer audiences. "This album is for the girls" means it is fun, camp, or emotionally cathartic. Inclusive and often used by people of any gender to signal vibe rather than literal audience. Not concerning. Common in pop-music and TV discussion. If your kid uses it constantly, ask them where they first heard it, not to police their speech but to understand which online community they are in.