I wouldn't worry too much about it. My beagle sits on our boxer all the time. I know it's a little ferret, and maybe was scary, but I think it's just a sort of, "Hey, how's it goin"?" kind of thing. When my beagle is being "chummy" with the Boxer, she with put her front paws on the Boxer's back and sort of "ride" her out the back door, while walking on her back feet. Other times, she will lay on top of her as if she is a handy couch! As long as the ferret isn't hurt and the beagle isn't acting "bossy", they should be ok. Just keep an eye on their interactions and gently tell her "No, we don't sit on little ferret people".