Well usually the snarl growl happens when she tries to play tug a war with it. but a lot of times we will get it just before she jumps to grab it if she doesn't get it she wallows in circles on the ground snarl growling till she either gets tired or gets a hold of it. Then its back to tug a war. (we have not encouraged tug a war i know its normal puppy play but we've heard from several places it encourages them to want to play tug with anything you try to take away from them so to only allow them to play tug with other dogs not people.
Edit: one morning she went on a mile walk i was taking her on our normal block and a half walk to the light and she was so energetic we wound up on a mile long circle walk (yes i had water and let her sit and rest) she just kept going so i went a route i knew and she was small enough at the time i could have carried her the rest of the way had she given up. that was our one good walk the rest are a fight.
I think if you keep at it eventually she'll stop, unless there's something else that's going on. It's really important to give no positive reinforcement for the behavior.
Klaus went through this stage for quite a while and it was fairly frustrating. I feel your pain.
I'm with the others on the rolling thing. It's not something that has a practical every day application. I think possibly it has been used effectively by people at some point, here and there. But I've never seen it work to do anything except either tick off or terrify a dog. And neither of those frames of mind are conducive to training.