ya it takes them awhile to learn, but if you are persistent, then they catch on eventually. I practiced inside my house with a leash. Its much easier for them that way first bc they are familiar with their surroundings. when you walk outside they have a lot more distractions and smells so they want to run around and sniff everything. its good your baby is young, you can teach her better. but some of the pups in my class that were too young kinda like your pup would just lay down in the middle of walking and not want to budge anymore. I think they are just too young thats why. all the other dogs would walk fine except for the one that was only a few weeks old.
I got my dog in the winter so i never tried walking here when she was that young. they told us to always have them walk on one side to avoid them running all over back and forth. they also said not to put strain on the leash, bc their natural insticnt is to pull harder if they feel they are being pulled. they really really enforce this in class, b/c they said its the main way to show your dog you are the leader, since the leader always walks first. here i found a good video you can watch to teach you how to loose leash walk.... its not the exact same technique my class taught, but same concept.