Rhiannon Davies (nee. Jones) was the sister of Torchwood member Ianto Jones.
Biography
Rhiannon and her husband lived on the Cromwell council estate with their two children David and Mica. Both children were amongst those briefly taken over by the 456. She had not seen much of Ianto before the 456 event, but they had apparently kept in touch.
Rhiannon was more open emotionally than her brother. It is unknown who was the elder sibling, but at one point she took a mature attitude with him about leaving the family just after their father died, thinking he did not care about them anymore. She also seemed accepting of his relationship with Jack and even comforted him when he told her he was not entirely sure what sort of relationship it was.
She was not aware that her brother worked for Torchwood, instead thinking he was a civil servant. (TW: Children of Earth)