Melanie Bush

Melanie Bush, or simply Mel, was a computer programmer from the 20th century and a companion of the Sixth and Seventh Doctors.

Personality
Mel was a computer programmer from the 20th century who came from the village of Pease Pottage in West Sussex, England. She had an eidetic memory, and a cheery, almost perky personality. She greeted most situations with a warm smile and good humour, and was an optimist whose views extended to believing the best of people's natures, but could also scream with the best of them. She was a health enthusiast and a vegetarian, often encouraging the slightly portly Sixth Doctor to exercise more. She was present (albeit unconscious at the time) when the Sixth Doctor regenerated into his seventh incarnation, and continued to travel with him.

Meeting the Doctor, for the first time
The Doctor first met Mel in Brighton in 1989. (PDA: Business Unusual)

Meeting the Doctor during his trial
Mel first appeared when she and the Sixth Doctor had been travelling together for some time. The events of were shown as part of a Matrix projection of future events being shown to the Sixth Doctor, so from his point of view, he was seeing an adventure he would have with Mel even before he met her in his own timeline. (DW: The Trial of a Time Lord)

Following the trial
Following his trial the Doctor returned Mel to her original timeline with his future self during an adventure on the planet Oxyveguramosa. (MA: Time of Your Life)

She decided to stay on Iceworld with the galactic confidence trickster, Sabalom Glitz, leaving the Seventh Doctor to travel on with his new companion, Ace.

Encounter with the Seventh Doctor following her departure
Encountering the Seventh Doctor he revealed to her that he manipulated her to depart his company on Iceworld because he knew what was coming (as Time's Champion) and couldn't have her as a companion. (NA: Head Games)

Following this encounter she returns to Pease Pottage. (PDA: Business Unusual)

At some point in the future Mel may have ended up on the planet Heritage, where she dies in the 61st Century. However during this point in the Doctor's adventures many enemies were attempting to eliminate his companions from the timeline, thus she may not have died here. (PDA: Heritage)

Alternate Timelines
Mel also encountered the Valeyard in an alternate version of the timeline, here she was much more cynical and hard than she had been originally. (DWU: He Jests at Scars...)