I think a lot of it is stemming from a friend sharing the Mayim Bialik video where she states that using "girl" implies being inferior to men. I don't agree with this at all and think some people are just WAY too sensitive about these things. I think this article sums it up pretty well:
https://nypost.com/2017/04/09/no-the-word-girl-is-not-an-anti-woman/
Eh, I think the article is a bit disingenuious to use song lyrics as its examples (particularly song lyrics where "girls" are matched with "boys," as there's a logical parity there).
I"m not going to waste my energy on a long rant with all the details, but I currently work in an office where the mysogyny runs as thick as molasses (and yes, I'm seeking other employment).
Every morning, our head of maintenance comes into the office for a cup of coffee. And every morning, he says, "Morning, girls." to the women in the main office (and he can say it to ALL the women in the office, because we're all clumped together in one central area, while literally EVERY man in the company has his own office space).
It IS demeaning. If I walked into a roomful of grown-ass, professional men every damned day and said, "Morning, boys" ... well, I'd probably sound like an old-timey hooker ... but it would also come across as condescending.
He could say, "good morning everybody," or "good morning all" or even just plain, "Good morning," and it would be fine, but he chooses to go with "girls," because he doesn't think of us as equals worthy of respect. (I have far more evidence of this than simple word choice, but going into detail would completely derail the thread). He's basically bulletproof, he's been here forever and the owner seems blind to his faults, so there's no point in actually addressing the issue, but when the hateful "girls" is tacked onto his morning greeting, I make it a point to not respond.
I have no issues with actual "girls" being called "girls," and teenage girls are still girls, so for the purposes of your story, I think you're fine. (I also wouldn't bat an eye at teenage boys being called "boys"). I just wanted to point out that calling women "girls" can absolutely be belittling in a professional environment, and checking for parity is a good test to see if it's appropriate. If your characters were gender-swapped, would you be comfortable referring to them as "boys?" If so, I'd say go ahead and use "girls." If not, consider a different term.
(It's not always an age-related thing, either. I wouldn't bat an eye at the term "girls night out," because the male counterpart is a "boys night out.")
Sorry for the ramble. It's a more complicated issue than it seems on the surface.