I think there is only one episode she is not in, The Great Egg Adventure. Instead of Ruby, Cera and Spike they have the 3 bullies from the 3rd movie.
She has 2 episodes where she is the main focus character. The Star Day Celebration, and Return to Hanging Rock.
It's not been revealed how she and Chomper became friends, exactly how this happened, where his parents are or why she was asked to look after him. Nor how he came to be accepted by all of the adults, especially Cera's father. He must have done something like saving her life, her little sister or something like that for him to accept Chomper would be one of my guesses.