It's a shame that people have to think this way, but it's probably more for your DH's protection than for your DD's friend.
We had a young boy knock on our door and claim to be lost. He was about ten or eleven, and he wanted us to drive him to the other side of town to his Mum's house.
He didn't know her name, or the address, although he said he could find the house. We didn't drive him or let him into our house. We rang 101 to ask for advice, were told to keep him with us and they would probably be with us within the hour. I said we were all outside in the garden, because we didn't want to encourage him to go into strange houses or cars, but also we didn't want to put ourselves in the position where he could say something happened in the house.
They agreed this was a good idea. Five minutes later we had three police cars with blue lights on coming at us from all directions because he was missing from a children's home and 'known' to the police.
They didn't tell us much about him, but they did say we did the right thing in not taking him to his mum as he would have been at risk in that house. They also said we did the right thing in staying outside with him.
I can see where your DH is coming from in worrying about being alone with a young girl. It's a shame but it's how things are now. I remember SIL refusing to let DH change her DD's nappy when they were at our house once. We had DS by then, so DH was used to nappies and this is our niece, with SIL and BIL, me, and four other children in the room, but even so, SIL wasn't comfortable with it and we had to respect it.