In the early seasons, Mary-Ellen was a tomyboy drama queen: she always wanted everything to go her way and was constantly teased by her brothers for this. She would play baseball with the boys, and would often get into fights with other kids. She had aspirations to become rich, famous, and have the ability to travel anywhere in world, leaving the "boring lifestyle" on Walton's Mountain behind. She was often romanced by guys older than her.
Despite her vibrant personality, Mary-Ellen becomes extremely mature in later seasons, often being the voice of reason behind her siblings.