Here is the passage again:
Chewing the dry, tough, whole-grain bread bought from
the health food store. Lorena tried to enjoy her lunch. Fantasizing
about a juicy cheeseburger on a soft white bun did not improve the taste
of the soy product sandwiched between leaves of organic lettuce.
The first part is a participle phrase fragment. There is no main clause between chewing and store. Every sentence must contain at least one main clause. Way to go, grammar brain!