Grass Eating

Hi, I own an 8 month Jack Russell Terrier who likes to eat clumps of mowed grass, mixed with dirt. I don't believe that she acts this way to induce vomitting, since she is a happy dog, and never acts like she is ill. Is this a problem, or is it just a "puppy thing"? Am I possibly not feeding her enough food, and therefore she is eating grass to compensate for this? I feed my dog anywhere from 2/3 of a cup to a cup of dog food a day, plus treats.