Put her on a long leash outside and stand still. Let her mind wander away from you. The heart beat you see her mind drift you need to walk a few steps in the opposite direction and enthusiastically say "let's go!". If she doesn't move in your direction then give her a gentle pull on the leash until she moves one inch in your direction then release the pressure on the leash. If she stops before she reaches you then do it again. You might have to repeat this a number of times until she gets the message. Be very happy and have a small party when she joins up with you.
Repeat this drill several times until she responds more quickly each time you invite her to join up. Remembering that you only move a few steps away from her in the opposite direction but enough steps that she has to make an effort to keep up.
Its as though you are the center hub of a wheel and she needs to keep within a certain distance close to you. Each time you move she needs to move too. This keeps part of her mind on you while she is having fun exploring. The end result is that she will (typically) hover closer to you than she has in the past and her 'coming' will improve as well because now she is learning to keep you in her sights and not lose all focus due to interesting smells.
Love Them & Lead Them,
~Elizabeth & Doug
Dog Training the Way Nature Intended