dd is 13 and a couple of weeks ago, a friend's mum told me she'd seen a BBM chat on her dd's phone between the two girls and a boy my dd barely knows, which was v sexual in nature and lots of swearing - basically all from my dd (have seen messages, and the other two said nothing that bad, but dd was horrendous). I was cross/worried as:
a) we and the school have explained about not sending inappropriate messages/posting stuff online, because once it's out there, you can't get it back and it can haunt you/be posted elsewhere without your agreement etc
b) the sexual nature of the stuff gives a very misleading impression of her (she's entirely innocent in practice, although her knowledge is probably greater than I'd imagined 
) and potentially places her at risk as the boy (and his friends if he shows them the conversation), all of whom barely know dd, will imagine she is up for far more than she might wish to be
c) the messages and chats I've had since with dd seem to suggest she has only a very sketchy idea of 'normal' boy-girl interaction (she's at an all-girls school) - she said the messages were a 'joke', which they were, but I would NEVER make explicit sexual jokes/comments to a male I didn't fancy, just as 'banter' - let alone at 13. I have recently suspected she might have (mild) Aspergers - am concerned she just doesn't 'get' that her comments were inappropriate.
So -I banned dd from use of her phone for a month or until I felt I could trust her and also from computer except for homework (had been facebooking other boy and hogging computer to watch endless videos, so was killing two birds with one stone, 
).
dd thinks - not surprisingly - that I am B totally U - desperate to have her phone back. Whilst I think she's understood point a and maybe b, I really don't feel comfortable she's 'got' c at all... So am sticking to my guns until the month is up.
But I now have a new quandary - whilst out yesterday I forgot to 'hide' her phone properly, so she found it and it is obvious from activity on her messages that she has messaged the boy again, whilst banned from using the phone, and then wiped the messages, I think almost certainly to arrange a meet up after the last day of school next week. I had said she could go out with her (female) friends after school on the last day, but after this last step, am thinking of insisting she comes straight home - I really do not feel I can trust her. Should add, I don't mind her meeting the boys as such - all the messages I've seen from them sound fine - but it is her behaviour I am worried about.
Help - what should I do? Don't want to come across as too harsh, as she will just rebel - don't wish boys to be exciting as 'forbidden fruit' and it is too easy for her to be in contact with them another way anyway. But I am really concerned about her behaviour.