It most likely is allowed.

She’s a minor who is skipping school, apparently without her parents knowledge or permission, and your manager has become aware of this either because she’s shown up to work when she was supposed to be in school or she’s talked about skipping class while at work. It can very easily be argued that by skipping school and being somewhere without the knowledge or consent of a legally responsible adult is dangerous and that she is putting herself at risk by doing so.

Your manager is not legally required to keep your coworkers whereabouts from her parents, and in fact you could probably argue that she has more of a legal requirement to let them know where their minor child is. Same thing if there are concerns about her health and wellness. As a minor, she has very few privacy rights when it comes to her parents.

I’m not sure of the policy behind this, but this is entirely disrespectful. As a minor myself, my job and any concerns my manager has with me should be dealt with me directly. It’s the same as me going to the dm and snitching on every little nonpolicy behavior she does. I’m appalled