Stacy Townsend travelled with the Eighth Doctor and later, Ssard, the Ice Warrior whom she would marry.
Biography
Stacy was born in 2220. By 2246, she was a worker on a deep space haulage freighter, the Dreadnought, along with Bill, her fiancé. They hoped to get married at St. Christopher's Church in Norfolk. Then the Cybermen attacked. They captured Bill and subjected him to cyber-conversion. By the time the Doctor arrived in his TARDIS in response to the Dreadnought's distress signal, he could not save Bill, so she decided to join the Doctor on his travels. (RT: Dreadnought)
The TARDIS materialised on the planet Mars in 3998, where the Doctor and Stacy found themselves caught up in Ice Warrior infighting and politics. They met an Ice Warrior named Ssard who, after an adventure with the Doctor and Stacy, joined them on their travels. (RT: Ascendance, Descendance)
Stacy and Ssard eventually left the TARDIS and decided to live in Ssard's time period. The Doctor was invited to attend their wedding, which took place on Micawber's World in 3999. (EDA: Placebo Effect)