Mrs. Libby is an 8th grade honors English teacher appearing at the Lock-In in The Ugly Truth. When Greg couldn't guess a nickname for himself that started from the same letter as that of his first name, she gave him the nickname "Jolly Greg." Greg didn't like it as his name didn't start from "J" and according to him it sounded bad, but the turn passed over. Greg was also quite shocked since she is herself an English teacher.
- Diary of a Wimpy Kid: The Ugly Truth (First and only appearance)
- It's unknown why she thought of "Jolly Greg" even though J doesn't start with G, it's possible that it is because she didn't listened to the instructions.