Constance Jane was a 19th century psychic.
She was put through the temporal interferometry machine, which split her personality into three. The Eighth Doctor met one of them, Millie. After Nathaniel Chiltern retrieved all the parts of the machine, he put Jane through it again as a test. She was able to alter her past so she was never mentally fragmented, and had her personality reintegrated. The alteration to the timeline was minor enough to not cause any paradoxes. (PROSE: Camera Obscura)