She may outgrow it, or she may just be one of those dogs who were born without an "off" switch for their tummy! I knew one of those very well, and he'd eat paper towel if it had touched food, even though he was well fed!

Getting her lots of exercise may help keep her from wandering enough to find disgusting things to eat - a tired pup being a good pup - but keeping her on a chain when she is outdoors is a good idea regardless, so she isn't loose to get hit by a car or anything.

Have you done obedience training with her? Does she know the command "leave it?"