Risk management (including with kids) is considering the likelihood they’d be at risk, rather than presuming the worst possible scenario. That’s why many people take their kids in cars. They could be killed or maimed in a RTA. But they most likely won’t.
However, 10 is a little young. It’s still primary age and most kids at that age aren’t well equipped to know how to react in an emergency. For example, it’s not common for kids of that age to travel alone, even walking to school. Or to be left at home alone or looking after younger siblings. Plus, she doesn’t have a phone to contact you direct.
It also depends on whether you’ve been to the friend’s home. If you’ve never been invited there yourself, you haven’t had chance assess any dangers. A sex attacker is unlikely, but there could be other dangers: fire risks, medications lying around, unrestricted internet access, poor supervision, lack of hygiene, dangerous pets, risky visitors, irresponsible older siblings.
Suggest simply explaining to your DD that you think 10 is too young for sleepovers at a home you’ve never been to. But she’ll be allowed once she’s a teenager. All parents have different levels of comfort with agreeing to their kids’ requests. It varies from child to child. Some 10 year olds are pretty mature and confident. Others are still very childlike. As a parent the key is weighing up if it’s reasonable to say no and staying firm with what you feel comfortable with. Instinct can be a powerful thing.
I’d probably say yes, unless my instinct was telling me otherwise. But I think it’s reasonable to say no.