Encourage her to walk by your side as you set off and as soon as she walks ahead of you pat your leg, repeat the command you use (be it "heel", "close" whatever) and walk backwards until she is by your side again. Stop, praise quietly, and when she is calm give the command again and start to walk.
This will take a few times to settle into the dog's mind that by pulling she is delaying the walk and you will feel very silly at first so practice in the garden first. Move on to somewhere quiet next and she will get the idea.