Sensory compression vest

I've order my teen daughter a compression vest because I've realised she's been craving deep pressure, especially at school. Usually we use a weighted blanket or ear defenders for pressure on the head but a weighted blanket in this heat just dysregulates her more and usually she doesn't want to sit still with it. 

It's my first time of hearing about one and ordering one so I have many questions:

1. When should she use it, I was thinking when she's sensory seeking or dysregulated also during situations that cause great anxiety. But I don't want her to get used to it and want it more than normal. 

2. How long should she wear it at a time? 

Also talking about deep pressure, she craves it on her head, mainly at school and the way she gets this is by headbanging or putting her weighted blanket over face which is not safe and will refuse to take it off. Also ear defenders work if she needs them. But how can we safely get the input to her head. She will not let us, her family touch her, but is happy for teachers to if she's in a meltdown.