Missy is a main character on Young Sheldon. She is portrayed as a bratty 9-year-old who fights with Sheldon for attention from their parents. Sheldon gets all the attention because of his intelligence and for starting high school at such an early age. Missy is disrespectful and contemptuous towards Sheldon, wishing him to disappear and even showing signs of optimism when her parents considered getting a divorce, hoping she could get away from Sheldon and part with her mother. She relished seeing Sheldon have bad luck and being lonely at school. She and Sheldon shared a bedroom. In "Potato Salad, a Broomstick, and Dad's Whiskey", she successfully pulled a splinter out of Sheldon's finger using toy tweezers though she only did it to make Sheldon stop complaining rather than from a change of heart.
Unlike Sheldon, Missy displayed little to no interest or aptitude in schoolwork, finding it challenging, especially math. She preferred to watch TV the whole time she was home such as ALF, DuckTales, and Looney Tunes and ignored her homework.
Missy has a sweet tooth for candy. Her parents spoiled her on a daily basis by buying her sweets and letting Missy watch TV all day long.
- She calls Sheldon by his nickname, "Shelly", as does their mother.