Often a child will try to soothe themselves orally. This is actually a normal thing in young children. Actually eating it and destroying it with their teeth . . . not so much. But your grandchild may have an intense need to bite down. The idea would be to provide her with things to do so in an appropriate way. They make all sorts of items for this that are sold at various occupational therapy websites. Some are rubber bracelets, necklaces. Some are items that they hold and can chew. Some vibrate, some are textured. They make t's and p's in hard rubber for the older child to self soothe/bite. The nervous system acts in mysterious ways and can send a signal to a child to bite/chew to soothe. Help her out by giving her something that is acceptable.
Gina, I believe you speak of PICA. One of the things that people often say regarding pica is that it involves some nutrient deficiency. This is actually untrue. It is a psychiatric disorder under the anxiety umbrella in the DSM 4. It involves eating non food items such as dirt, rocks, ashes, hair, or whatever.
Hope this helps.
It's possible she is not getting enough of a certain nutrient in her diet. Frequently on paperwork you fill out for WIC or well-child check-ups they ask things like if your child ever eats non-food items like dirt, cigarette butts, etc. I would take her to the pediatrician and see what the doctor thinks. They should be able to run some labs on her to see if her iron, etc. is low.
Don't believe that this is really normal, but as I'm not a physician, I can't say for sure. The first thing that I would look into is "pica."
https://health.google.com/health/ref/Pica
talk to her pediatric about her behavior so that she can help i dont think this is normal