Gillian Rose Petra was a woman from the 21st century who travelled back in time to observe Sherlock Holmes as part of her doctorate in criminology. To this end she worked as a maid, Rose Donnelly, in the boarding house where Holmes lived with his friend John Watson, supplementing her income by playing guitar in the park. She also posed as Maria Tory, a widow of independent means whose guise Gillian assumed when she was in need of funds beyond that which she could earn as a maid or busker. On one occasion she followed Holmes disguised as a man, wearing a pair of old boots that had once belonged to him.
However, Gillian's patron Jimmy Moriarty had no interest in furthering her academic research but instead wished to ruin Sherlock Holmes' life, to test the bounds of destiny and determine whether an extraordinary man could remain extraordinary in diminished circumstances. Moriarty had told Gillian that he had invented the method of time travel used to send her in the past, but in actuality he'd obtained it through a pact with the Celestis. Gillian was implanted with a device that she originally thought was a birth control implant, but which she was later told was a "homing beacon" that would permit her to travel home coincident with the eruption of Mount Krakatoa. (PROSE: Erasing Sherlock)
After her disappearance during the eruption, Gillian (or perhaps some corrupted version of her) reappeared in the life of Sherlock Holmes some nine years later, in October of 1890. Both Holmes and Watson complained about being followed by a mysterious woman dressed in the same garb Gillian had worn as the "Widow Tory." However, this woman now seemed less than human, her veil revealing nothing of her face. Holmes thought she reminded him of a dog unused to walking upright. She delivered Holmes a package containing the pair of old boots that she had worn while following him nine years before. (PROSE: Erasing Sherlock Prologue)