Mary grew up on Mars, living with her parents in their apartment in Mars Dome One and by the age of four had inherited her mother's stubborn streak, her father's ability to drive people crazy and had developed a particular distaste for Swedish meatballs. As a child, her room was filled with Red Sox posters, stuffed animals, model starships, her mobile of jeuf that had been a gift from Delenn and would often have a scattering of click-bricks on the floor.
Her father would sometimes spend the day with her, teaching her to play baseball and even taking her for walks outside the dome. Though this made her mother Lise apprehensive, Michael insisted that Mars-kids needed to learn how to handle themselves outside at an early age in case of a dome rupture. For her part, Mary loved to walk outside and would beg to be taken out all day long.
By the time she was fourteen, Mary had become particularly fond of and proficient at tennis, which she played for her school team. She practiced with Stephen Franklin, whom she referred to affectionately as "Uncle Stephen," whenever he visited. Indeed, she beat her "uncle" when they played a game. She even asked him to play another game with her but Stephen was exhausted; much to Michael Garibaldi's amusement. She later won first place in her first tournament.