
im guessing that your young dog finds the unwanted behaviour (pulling) very rewarding, ie, she gets to where she is going much faster.
So, you need to take the reward out of the equation. When ever she pulls, stand still. Dont move off until she comes back to your side. Try to make her aware that when she is on a lead, she needs to be paying attention to YOU, and that she is responsible for keeping the lead slack.
You can also use a headcollar, or harness, (the kind for stopping pulling, not the normal kind, that will just help her pull you more effectively!)
Are you holding the lead correctly? i know it sounds a daft question, but if you hold the lead in one hand, and she is as far away from you as possible, she can also pull you more effectively, if she is on a shorter lead, its not so hard to hang on.
If you find a headcollar that suits you and the dog, (Halti, Gentle Leader, Dogmatic) use that to stop her pulling when you dont have the time for training, ie on the way to the park in a morning, and make specific times for lead training using a flat collar, or a half check collar.
That way you arent inadvertantly rewarding her when you are in a rush.
If you do use a headcollar/harness, please make sure u use a piece of chain, or rope to link the flat collar to the headcollar/harness, just in case of emergencys. Make sure that saftey rope/chain doesnt interfere with the action of the headcollar though.
Do you do clicker training? If not research it, its a reward based method of training, and its one dogs pick up on really quickly.
Other things u can try are, turning around when she gets ahead of you, walking backwards when she is in front, training discs, using a walking stick to trip her if she gets in front, there are lots of ideas out there.
Good luck,
Em