I lived in the centre of London when my daughters were growing up,which believe me brought lots of worries but a sleepover with groups of children did not mean sleeping with each other, the boys were in one room the girls in another..My granchildren still do this too. If the parents weren't there it would be different. Is this perhaps what your daughter means, it was one big giggle from start to finish and a way of growing up safely,of course trust is involved but I guess you have brought her up so that you can trust her.. be careful because one of the mothers in our community never let her daughter join in with the other children... guess which child ended up pregnant while still at school..