At the end of Andrew Clements' Frindle, after reading the letter Mrs. Granger had written him ten years ago, Nick comes to understand the significance of a comment Mrs. Granger made ten years ago about the ability to create new words by making them up; Nick comes to realize she actually supports Nick's ability to invent brand new things.
One comment in the letter that stirs his memory about earlier comments is her explanation for why she values the dictionary so much. She values it because, no matter how much change has occurred in the world, words are still persistently important:
Words are still needed by everyone. Words are used to think with, to write with, to dream with, to hope and pray with. And that is why I love the dictionary. It endures. And as you now know, it also changes and grows. (p. 86)
After reading her remark about changing and growing, he remembers her comment ten years ago that "words could be made up brand new, I suppose" (p. 41). He further remembers that, after she gave the long history of the origin of the word pen, he had asked, "And after all, didn't somebody just make up the word pinna, too?," which ignited a spark in her eye as she had asked, "Then you are not going to stop this?" (p. 41).
The words of her letter help him understand exactly why she had commented about making up words, remarked that he wasn't going to stop, and developed a spark in her eye: she was happy that he was not going to stop trying to rename a pen a frindle; she had been rooting for Nick's new word change all along. She firmly believed that if Nick kept pursuing calling a pen a frindle, the word frindle would be added to the dictionary, which was a success she wanted to see. Mrs. Granger admired Nick's creativity and knew he could accomplish great things with it; adding a new word to the dictionary would just be one small achievement among what Nick would be able to accomplish during his lifetime.