Child has a friend who own a pitbull

So as the title states my 8 year old daughter has a friend who owns a pitbull. I’ve never met the dog and I didn’t find out until I had already let her visit her friend at their house, which I admit was careless on my part, but thankfully nothing happened that day. Now my daughter wants to hangout with that friend again, but I’m not comfortable allowing her around that dog. I would be a nervous wreck the whole time she was there. Problem is how do I explain that to my child or even her friend’s parents when their daughter asks my daughter to go visit? The last few times they’ve asked I’ve just said we already had plans, but I’m sure they will catch on eventually that something else is going on. I’m afraid to cause conflict by saying anything about the dog because I’ve seen how absolutely nuts pit owners can get.