Treat like you would a puppy being trained to the lead. Put a soft collar on her, assuming she doesn't already wear one, and let her get used to that. Put , ideally, a long lead on her, leave it loose and have her come to you. Reward her with affection and, perhaps, treats when she does. Gradually get around to picking up the lead, but don't pull on it. If she pulls away, don't indulge in a tug of war, leave it. The idea is to let her go where she wants, you following with the lead or string as loose as possible. Then she is absorbed in what she is doing and not noticing you. You will find that she gradually adjusts to the occasional, gentle brief restraint, but since she's going where she wants, she ignores it. Tell her to come back to you once in a while and reward her. In time, she'll adjust to firmer control, and associate being on the lead with something pleasurable.
Now, I have trained wolfhounds this way, and believe me, even a puppy can pull you over, so you have to con them a bit to start with, like that.