DSD is 15 and has a key to both our house and her mum's. She sometimes lets herself in when we're not here, which is fine. Eg on her way between school and meeting friends later. But lately she has taken to coming round when we're not in (and she knows we're not in) with her boyfriend (16). I'm kind of uncomfortable about this - my own DCs are younger and that sort of thing hasn't arrisen yet.
They also shut themselves in her room together sometimes when I'm home on my own with the kids and I don't feel comfortable to tell her not to. DP thinks she's a sensible girl and that it's OK. Is it? And if not, what do I do about it? I'm not sure whether her mother knows where she is or that she's here.