Hi Rivergirl
Like Splash I only have one son who is double your daughters age so have never had this problem but I def wouldnt let her stay overnight , apart from the age difference which is huge, she hasnt known him very long either. I personally dont think he should be asking her to do this either but then maybe he dosnt know her true age?
Good luck anyway, our children are so precious to us and we want to protect them but its very difficult at this age...