My brother has a pit mix who is about 90lbs and I have 2 yorkies. I have dog sitted his dog for weeks at a time in my little condo. She was GREAT with my dogs. I had no problems at all. However when I was not home they were not left together alone. She was put in the finished basement for the day and my dogs were gated into the kitchen for the day... JUSSTTT in case!
One time they 'broke' out when I was out... i came home to trash all over my house. His dog broke out of the basement, pushed my dogs gates aside and all 3 had run of the house, they went through the trash and made a mess. But noone was hurt or sick when I got home so I guess shed be ok with them alone.