I have worked as a teacher for many years and have had my share of altercations. How long do you think I would last as a teacher if I picked up a student and dropped them on their head?
Any guard worth his salt should be able to deal with an unruly 15 year old girl with ease.
Yup. With ease, and sometimes by dropping her on her head. Age doesn't matter. Gender doesn't matter. Physical size doesn't matter. Violence will be contained as quickly and as thoroughly as possible. If the violence turns toward me, I will stop the violence by whatever means I can. I am allowed to protect myself even when it is my job to protect others.
I've worked as a security guard for many years and have had my share and yours of altercations. You dont want any part of a 15 year old girl coming at you. Sometimes you have to drop someone on their head to get them to stop fighting. I will never second-guess anyone's successful self-defense or security choices unless I was actually there for the whole situation.