Gwyneth (The Unquiet Dead)

Gwyneth was a servant girl at Gabriel Sneed's home in Cardiff who had clairvoyant abilities.

Profile
Gwen Cooper said that her family had lived in Cardiff for centuries, implying that (although Gwyneth did not apparently have children), she might have Gwyneth as an indirect ancestor. (DW: Journey's End)

When Gwyneth gave the Doctor a cup of tea, she said, "Two sugar, sir. Just as you like it", although she had never met him before. These powers enabled her to be contacted by the Gelth who had arrived in the city via a space-time rift located there. She believed them to be angels. When she stood underneath an archway in order to contact the Gelth, they passed through, and trapped the Doctor and Rose. To destroy them, she struck a match once the Doctor and Rose had escaped, igniting the chamber and destroying herself in the process.

Her actions appeared to be suicide until the Doctor told Rose that Gwyneth was already dead ever since stepping into the archway; even when she had told him that she would light the match. This refers to her abilities once more. (DW: The Unquiet Dead)

Gwyneth's genetic traits would be passed, through the space-time rift via spatial genetic multiplicity to Gwen Cooper an agent of Torchwood 3, a branch of the Torchwood Institute based in Cardiff. Gwen and Gwyneth looked very similar. (DW: Journey's End).

Behind the Scenes
Though Eve Myles played both Gwen and Gwyneth, Russell T. Davies denied in a Doctor Who Magazine interview that they were in any way related. However he reversed this position in Journey's End by having the Doctor and Rose Tyler comment on the resemblance and the Doctor explaining it and Gwen saying her family had lived in Cardiff for centuries.