My son also takes piano and what his teacher did was provide him with either more work to progress more quickly or let him pick a fun song to learn on his own from his fun book. He also uses Faber books.
What I have noticed with Faber is that you're taught a basic song. It may come back in later books with the chords. If you have a song you liked playing (and it's a classic), you can probably find sheet music on your own online that is more than just a basic melody. We did that with 'Ode to Joy'.
If you need a challenge, please approach your teacher and don't feel shy. She may be able to best assist you in appropriate sheet music. Perhaps there's something you would like to learn for the holidays or just for fun?
Editing to add: How are your dynamics? Are you playing things perfectly at each lesson? You can use these to justify her adding more work to get you through faster or giving you a harder piece to work with for a few weeks. Also, my son flew through the first few books really quickly, but slowed down some on the harder material. His lessons are a half-hour. If yours are longer, you may be covering more material than him.
Good luck and keep practicing
