its so hard isnt it
i think you said the right things to DD you told her the truth, my DS made a friend with a kid that sounds similar to your DD's friends and after i ment his friends mum and she told me about the limited to no supervision she gives her kids(10 and 11) because they are old enough to look after themselves I just explained my reason to DS that he wouldnt be going to their house for play he understood.