Read THIS. It will give you an idea of what most of the people here think about shock collars (myself included).
I agree that you should get her enrolled in some sort of an obedience class asap. This is one of the first things I do whenever I get a new dog.
So many of my friends ask me how come my dogs behave so well....I take them all to school. Can't expect them to do what you want unless you teach them

Good luck!

P.S. As for the long puppy hood of labs, they're right up there with the long puppy hoods of mastiff's. Bon's almost 2 and he's still a big puppy, but he probably weighs in at 150-160 pounds