I used them from age 11, with a lot of help from lube and older girls in ballet. Get her to ask and get help from her team mates. The elder ones should be able to well help her along, quite graphically. They got us newbies in the changing room and we'd sit on the benches or lay on them till we got it.
A syncronised swimmer of that age will likely have had a lot of ballet and might not have a hymen at all.
The girls in ballet instructed me to get hold of Tampax with a plastic applicator and lubricate it with Vaseline for the first time.
I don't recall ever feeling a hymen as even by that age I was doing full splits.
At 15, I was fully en pointe and doing complex centre work, which continued when I moved to France for a year abroad with little problem, all the moves were in French, and it wasn't hard to get a place in class. Most of the girls in my class then weren't even virgins, I was one of the last to be so.
Pads, so gross and you could see them through leotards, it wasn't going to work.
As her what her teammates do.
YANBU. But IME the girls all got instruction from one another v. their mothers.