Mary is a human passenger aboard the Axiom.
While doing her usual business around the Axiom, Mary was talking to a friend via hologram as she boarded a monorail-type transport. WALL•E, who at that time was looking for EVE, wanted to get past her to reach where she was. Mary, without knowing WALL•E was behind her, pushed her hover chair back and pushed against WALL•E. WALL•E made it, and easily escaped. As there was no room to reach EVE, he wanted to get Mary's attention. He eventually shut off the hologram communications, and Mary's clothes changed from blue to a regular red. When she noticed this, she acted as if this was the first time she saw the Axiom, which it probably was. What she also noticed soon after was WALL•E, and told her his name, and she told her's. As WALL•E informed her of EVE, and telling if she could let him past, she kindly pushed her chair back so he could get through. As the transport arrived at the Lido Deck and the passengers got off, Mary took notice of the gigantic pool located on the Lido Deck that nobody else even noticed their entire lives behind their messaging holograms.
While at the windows, Mary was glancing at the stars, and during that she noticed WALL•E space dancing with EVE in space with a fire extinguisher. Soon after noticing, she accidentally pushed her hover chair back and bumped into another passenger, John, who also met the robot. Upon seeing each other, they quickly fall in love. They are later seen on the Lido Deck late at night when no one else is around, playfully splashing in the pool, against the objections of a robotic life guard that John playfully splashed to shut it up; shorting it out in the process.
When AUTO tipped the ship over to prevent The Plant from being placed inside of the Holodetector, Mary and John saved a bunch of babies that fell out of their hoverchairs as they themselves were, she then observed with the rest of the Axiom Passengers as Captain McCrea stood up and charged at AUTO and deactivated him to right the ship again. She then helped with bringing The Plant over to the Holodetector as the Axiom made its jump heading back to Earth. Mary then departed the Axiom with the rest of its passengers; becoming one of the first Humans to have ever stood on Earth in over 700 years.