
This is a common problem with small children and puppies. Naturally the child wants to treat the pup as a toy, but equally naturally, the pup isn't having any of that! It can take a long time to teach a very young child that the pup
isn't a toy, but a real, living entity, with likes and dislikes, and good moods and bad moods, just like them. You are absolutely right to keep them apart when you can't supervise, because there is a very real possibility that either could unintentionally hurt the other.
Puppies are also very attracted to small children, simply because they act more like puppies than older people do! They make jerky movements, they squeal, they get excited - all of which a pup can relate to, and wants to join in. To make the puppy calm around the child, the child has to learn to be calm around the puppy. Not easy to do, I know. Don't forget the puppy is also very young still, and is too immature to react in any way other than instinctively.
At the puppy party, what led up to the growling? Were other puppies annoying her? If so, what were their owners doing about it? With a bitch puppy, it's unlikely to be a case of too much testosterone! There is a possibility that Meg feels she is being bullied by her littermates (that's you and your family now, of course), or it's more likely that she felt insecure there and was scared.
I think what I would do to get your daughter and the pup more pally would be to have your daughter hold Meg's bowl just off the floor while Meg eats (with you holding over her hands too), and not picking Meg up for cuddles at all. Get her to stroke Meg gently and slowly when Meg is feeling sleepy, and to stop before Meg wants to play again. As they both grow and mature, things will settle down. Don't rush things, though - don't expect either of them to act 'grown-up' before their time.
:)