It is tricky, because you are essentially saying to your children, "I don't trust your friend's parents". It's a tricky one, the idea that friends' parents are not to be trusted. When first learning about "stranger danger" and "don't talk to strangers" as it was then, I remember thinking "but that means everyone around me is a stranger". Childhood logic. I used to say to people such as my parents' friends (when I was 6) "I can't talk to you, you're a stranger".
In the end, how long do you keep trying to protect your children from every eventuality? Where do you draw the line? As others have said, the "danger" you are fearing is not limited to sleepovers: it can happen on days out, Brownie overnight stays, foreign language exchanges, school residential trips. (Do host families in foreign languages exchange trips have to be DBS checked, nowadays? Also host families of au pairs?) I went on a German exchange aged 14: if these risks crossed my parents' minds, I never knew, although they were alarmed to hear afterwards that somebody took me on a motorbike. The danger of that didn't occur to me at the time, at all. Other children on the trip had to cycle to school on dark mornings, when the temperature was -2; should their parents have been up in arms about the icy roads, and the cold?
When I was fifteen, I went on a two-week trip abroad involving boys and girls, all staying in the same house, but in separate rooms. My parents told me to look out for myself, and made sure that I knew about contraception, "just in case", and gave me some to take with me, but they certainly didn't prevent me going. (For the record, absolutely nothing untoward happened!)
For the age group here, your DD might not know why you are anxious about this, and might parrot what you do tell her, which could have other consequences. This is an extreme example (as extreme as abuse actually happening), but if a child was to hear "you can't stay at your friend's house overnight, because I don't know her parents well enough", that child might repeat to her friends "Sorry I can't come, my mum says she doesn't know your parents well enough", which might in turn get back to the parents. The children might not understand the implication, but the other parents will; the idea of abuse might not even have crossed their minds, and they might in turn be angry at the accusation, and say to their children "now we are forbidding you to be friends with them, because they think we might do something to you". An extreme idea I know, but it's an example of how being over-protective can have unintended consequences. Something like "she thinks your parents are paedos" could easily spread around the whole group, if not handled carefully, leaving somebody ostracised from the whole group.
Some replies here have suggested saying "you're not going to anyone else's sleepover, but we can have them here". Why should a parent saying this be more trustworthy than any other parent? Would all the adults in the host's house have to be DBS checked? "I can't trust other parents, but they can trust me." Think about it.
Sooner or later, children have to branch out on their own, and go to places overnight. I agree with @Runnersandtoms suggestion about using the opportunity to teach her about bodily autonomy; if she has a phone, tell her to confirm at bedtime that she is OK, and offer her the opportunity of fetching her in the night, no questions asked. The world is full of risk, and I think it does children a disservice to try too hard to protect them from every eventuality.