Played by Raegan Revord 

Missy (Melissa) is Sheldon's twin sister. 

Missy doesn't share Sheldon's exceptional intelligence, but she's a very intuitive child. 

Sometimes Missy teases Sheldon with her older brother Georgie, but mostly the twins have a special bond. 

The confide in each other, Missy would be lost without Sheldon, and vice versa.