Adeola Oshodi

Adeola Oshodi, a cousin of Martha Jones, was a technician at Torchwood 1, where she worked on the free energy project. She died as the result of Cyberman infiltration of Torchwood Tower.

Biography
She was finding a place to make a romantic liaison with a co-worker when she was cybernetically altered by Cybermen who were able to slip through the Void through a breach in space-time. Her 'upgrade' was internal, through an EarPod-like earpiece (or earpieces) linked with connective tissue directly to her brain. She was killed definitively when her earpiece(s) were overloaded by a signal from the Doctor. (DW: Army of Ghosts)

Her cousin, Martha Jones, with whom she shared a strong resemblance, would later travel with the Doctor. (DW: Smith and Jones, NSA: Made of Steel) It is not known if the Doctor ever told her how Adeola died. Like Adeola, Martha would later come to work with a branch of Torchwood.

Known family
Adeola was the cousin of Martha Jones. Her aunt and uncle were Francine and Clive Jones. Her other cousins were Tish Jones and Leo Jones. Leo's daughter, Keisha Jones, was Adeola's cousin once removed. (source?)

Behind the Scenes
Actress Freema Agyeman played the parts of both Adeola and Martha. The confirmation that the two characters were related first became public in the Made of Steel novella which was actually released prior to the broadcast of Smith and Jones. (Made of Steel takes place after Smith and Jones and introduces the character.)

This isn't the first time that an actor guest-starred in the series in one role, only to return later as a recurring character in another role. Past precedent includes Nicholas Courtney, Lalla Ward and Colin Baker, all of whom appeared in different roles before becoming regulars as The Brigadier, Romana II and the Sixth Doctor, respectively.