I'm dealing with a 3 year old Shep/Lab cross that's totally new to civilation and does the exact same thing. He was rescued from a very rural place, brought to the big city and has no idea what a leash is all about. If he sees something like a strange person, dog, machinery or gets too far from my place, he won't budge. I'm thinking it's just a whole lot for him to take in at once. He's not fearful, just overwhelmed by all the sudden changes in his life.
We started with walks around the yard and having lots of ''fun'' with that. No yanking or pulling, just fun and some treats when he walked with me. Next, we went out of the yard and just looked around the alley. Again, fun treats and praise when he came along. Now, after 2 weeks, he's walking nicely around the block with lots of sniff breaks when he finds sonething interesting. As we progress, the treats become fewer because of his growing confidence and interest in his new environment. It's my ''job'' to be the most interesting thing in his life and worthy of his trust.
Another thing to keep in mind is the importance of lots of socialization before she turns 16 weeks. If you can, find a really good, positive reward trainer in your area that has puppy get-togethers. If nothing is available, see if you can find people you can hang with that have steady minded adult dogs that your pup can interact with safely. And also introduce her to as many different people and places you can. In the long run, doing this NOW will will serve both of you very well.
Wish you the best with your new pup!