Miranda

Miranda is an artificial human controlled by Deus Ex

Creation
Miranda was created by the Lucian Alliance as part of a project to create a completely loyal supersoldier. Upon her activation, however, she became rampant and destroyed the research station she was on. She fled to the planet Nimoy where her lack of understanding rendered her a social pariah.

Joining Serenity
When Serenity landed on Nimoy, Miranda snuck onboard the ship, which left with her stowed away. She was revealed to the crew after some engine works she was attempting backfired, burning her hands. Despite some initial protesting from the crew, she fit in rather well as Serenity's mechanic.

Battle of Terra Vita
During the battle of Terra Vita, Miranda piloted a heavy mech. She used it to great effectiveness, destroying multiple Carriers and saving Samantha Endesha's life. The mech was left for the Terra Vitan army to use when Serenity left Terra Vita

Destruction of Serenity
When Serenity was destroyed, Miranda and the rest of the crew HALO jumped. During the fall John Shepard's mind somehow entered her body. It is not known what happened to Miranda's mind.

Trivia

 * Miranda is named after the character from the Shakespeare play The Tempest. Her first words were a quote from the aforementioned play.