Hi, I would have a close look at her diet, dogs that are fed on a complete dried meal, tend to find poo very tasty. i feed my dogs complete food but out of 4 only 1 finds it tasty, the only thing you can do, is stop her doing it by not letting her off the lead and cleaning up after her. Try giving her a bone to chew on and raw chicken wings, this did stop mine for a couple of days, i also give raw carrots, brocoli and they love bananas...a bit of variation might help.
there is a train of thought that says it is the dogs way of saying they are lacking something...
Good luck.