Sister Chastity was a member of the Threshold. She killed Marquez on Icarus Falling so she could keep the box of Time Lord secrets. (COMIC: Fire and Brimstone) The Eighth Doctor encountered her again on the Threshold base of Wormwood, where she was killed by Abraham White. (COMIC: Wormwood)
Izzy Sinclair recalled her when reminiscing on her adventures with the Doctor after returning to Stockbridge. (COMIC: Oblivion)