
Has she always done this, or is it a habit she's just developed? If she's always done it, you need to start training her again to walk properly on a lead. Most people have the opposite problem of trying to stop the dog pulling them!
You'll have to start giving her an incentive to move, if she likes food, take some of her favourite titbits with you & when she stops, call her name with a gentle tug on the lead & entice her forward with the titbit.
When she is walking OK, don't forget to praise her.
Some dogs are like donkeys, when they feel the tug on the lead, they dig their heels in, so you have to use the dog equivalent of a carrot, to get them moving again.
When you are walking, don't go at her speed, but a fairly brisk walk, so she has to work to keep up, keep talking to her in a brisk bright way (you'll get some funny looks!), just to keep her interest in you not in the smells or whatever she wants to stop for.
If she's just started doing it, get her checked by the vet as she may have some perfectly good reason for not wanting to walk.