Tell her parents that it was your phone and she was borrowing it. Then, if they give it back (which, if they don't, you could take legal action for stealing 'your' phone) you can give it back to her and have her hide it better? If you bought it and the service, chances are it is in your name.
Which means it is your property and they took it without permission. Which is technically stealing.
As a parent there is no way on planet earth that any other person or official or whomever would tell me how to deal with my children - not a chance in hell. So I must therefore agree with your friends parents. That said there must be more to this because it seems irrational to take a phone from a 17 year old.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.