In the early 2360s, she was an ensign on the USS Victory. In 2362, she was part of an away team commanded by Susanna Leijten along with Geordi La Forge, Paul Hickman and Anthony Brevelle. They investigated the disappearance of a science team on Tarchannen III. While on the planet, the entire team was unknowingly infected with an alien DNA.
By 2367, she transferred to the USS Aries. In 2367 the virus which had infected Mendez began to take effect, compelling her to return to Tarchannen III. Without warning she stole the shuttlepod Cousteau from the Aries and flew to the planet; her crewmates reporting that she seemed perfectly normal just an hour before her disappearance.
By the time the crew of the USS Enterprise-D had determined the cause of her flight, it was too late to save her as the metamorphosis had completed and thereby made the changes irreversible. (TNG: "Identity Crisis")