What Breed Is My Dog?

This is a rescue pup I've recently adopted. She's 9 weeks old and the shelter believed she was likely a Black Lab Collie x. They said her mum looked like a Black Lab, but with a tiny bit of white on her chest and was relatively small (smaller than a Border Collie). They didn't see the dad, but were told he looked similar to mum. However the owner, who I'm told is not great with dog breeds reckons the mum was actually a Lab Mastiff x and the dad a Lab Pit Bull x. What do you reckon?

One of her siblings actually does look very Lab/Collie like with a smaller up-turned nose and more narrow face. The other puppies were more like our pup, but with maybe a slightly longer face shape. I know it's hard to tell, but am wondering if anyone has an idea? She's quite a dominant pup and definitely has Lab tendancies - very greedy! So it would be good to know if she's got Mastiff/Pitty in her so we prepare ourselves to handle that tougher and more protective side of her nature, especially with small children and other dogs around. Thanks!