It would be helpful if you say 1 )you wanna to go
or 2) dont want her to go
or 3) want to get one across her mother
however if she is over 16 which you say it looks as tho she can:
see here:
http://www.childline.org.uk/Explore/CrimeLaw/Pages/Rights.aspx
I dont think you can argue it is covered by leaving home or leaving school
In th good old days - 1968 I wandered around Italy - youth hostels - when I was 16 and no one gave a t+ss. I got rather good at Italian.
( al fine, uscimo arriveder le stelle and so on )