Tell her that she has to tell her mum and the Cadet leaders.
Explain to her it would be better if it came from her but tell her if she doesn't tell her mum by a set time (a day or two) you'll have to tell her, as no-one has the right to hit her. Explain that you are doing it to protect her and not to get her in more trouble. But try to make her feel like she's in control. Tell her you (if possible) would be happy to come round and give her a bit of moral support and help broach the subject with her mum or help her write a letter for her mum to read if she doesn't feel she would be able to talk about it. She might find once she starts to write it down, it'll all come pouring out.
And for god sake, if you do have to tell the mother, don't do it by email, phone her or go round.
( Maffers I flow kinda strange like Spina Bifida footprints, Mon 18 May 2009, 10:46, Reply)