What does your vet say? Is your puppy otherwise healthy and gaining weight appropriately? How are her poops? Could her diet be deficient in some nutrients? Does she have access to other fresh foods?
Here are some good resources for you:
Dogs and cats are often observed eating grass and other plants of no apparent value.
www.dvm360.com
The question may be simple, but the answer is not. Nevertheless, here are a few reasons your veterinarian will discuss when you pose the question, Why does my dog eat grass?
vcahospitals.com
mucus
www.whole-dog-journal.com
radish sprouts
www.whole-dog-journal.com
Peggy's munched soil for as long as we've had her. In fact, all the puppies in her puppy class loved snatching mouthfuls of mole hill dirt when they were playing outside. It's not uncommon for Peggy to enjoy some grass on occasion, too.
When she was vomiting frequently as a puppy, it was because she wasn't digesting her food properly. Have you considered switching up your puppy's diet? What is she currently eating?
Puppies also just generally explore the world with their mouths, and if they lack other activities/stimulation while they're outside, the most interesting thing will be whatever they can find on the ground. If the behaviour gets your attention, even better! In excess, this can definitely lead to tummy upset (or worse) so you want to try and be the most interesting thing in your puppy's world. Play lots of "follow me" games and have safe toys and chews available at all times, especially during teething.
Also practise
lots of trading. You want your puppy to hear the words "leave it" and think "Oh yay!! My human's got something even BETTER for me! And wow! I get to have the original item, too?!" (Only if it's safe, of course.)
This is actually something we're working on over in our monthly trick club. Just click the link in my signature to follow along.