It doesn't mean she is aggressive because she won't let you hold her on her back. It means that the breeder probably didn't do it. It is something that will probably come with trust. I wouldn't force her to do it right now. She is going through so many changes. Just take your time with that one and slowly start doing it by just having her tipped back a little near your armpit and work your way to having her feel comfortable laying on her back. Rub her belly and talk nice and sweet and calm to her while doing this if it is a goal of yours. Please don't be forceful with her right now. You will regret it later when she doesn't trust your hands or you. When she gets a little older and you have built a trusting, loving relationship then it is fine to do that with your hand and even recommended. As far as your big dog goes, your little one doesn't see any difference in their size whatsoever
