Nacy,
She's not too young. She's trying to be boss. When they are that young you don't want to put them on any kind of lead for long periods of time. Try for 5 minutes and give lots of praise and treats if she walks with you. If you have to drag her then go ahead and drag, but I have found that small liver treats are a great incentive. Hold one close to your side as you walk, but don't let her eat it until she walks a few steps with you. Give her time, patience, and treats and she'll get the message given time.
Also, if you have a dog obedience school nearby I would recommend taking her there as well. She should be learning to sit, stay, come, and down and now is the best time to start training for both of you. You need to learn how to teach her and she needs to know who's in charge. Plus it really helps with socialization skills for your lab. They love to be around other puppies. Good Luck!!!