We don't use 13 year old kids to teach or do anything else for that matter. There are schools that have the kids sweep and clean the dojo. That isn't us. My son started to teach children at age 14 but by that time he had been training for 6 years held a black belt and was never unsupervised. He was paid and his tuition was covered. He did teach five days a week after school but was home every night in time to do his school work. Working there was his choice and kept it up till he was in college and he will still stop in and teach a class or two if he is in town and his schedule permits.
I don't see any problem with a 13 year old with experience helping the younger kids before class with their homework if she is compensated and supervised. We do get kids who are dropped off after school by the school bus and are there an hour or more before class so help would be appreciated.
But this child isn't experienced. As far as talking to both parents that isn't often an option. We get kids who are brought by mothers, grandparents, and siblings, fathers are rare.
We teach in a fishbowl there is no place on the floor that cannot be seen by the parents and staff and parents are welcome and encouraged to stay.