Mary Warner

 was an East End prostitute and the original fifth and final victim of Jack the Ripper.

Mary Warner lived at Miller's Court like her friend Mary Kelly. Ripper lore placed her at Ten Bells pub at some point. On 30 September, 1888, she was at the pub with Kelly. The landlord Bert kicked them both out around 7 am. In the original timeline, she was murdered and found in her bedroom on 9 November. Her death forced the Metropolitan Police Service and City of London Police to acknowledge their mistakes and begin working together. (COMIC: Ripper's Curse)

An old police photo seen by Christine Summerfield showed the victim sprawled out on her bed. Parts of her body had been hacked off and her head had been ripped up. (PROSE: Dead Romance) Rumours of the time were that the police believed it more likely to be a demon or wild beast that did it. Ace had seen the Seventh Doctor at Miller's Court at the time, controlled by the Valeyard.

The Seventh Doctor couldn't remember killing her but said that time may have forced the events because those five particular women had to die. (PROSE: Matrix) The Eleventh Doctor told Amy Pond that the victims were static points. If Mary lived, the Ripper might continue to kill or she might go on to give birth to another Hitler.

Amy tried to warn Mary Warner, anyways. The Doctor changed his mind and organised a stakeout at Miller's Court with Frederick Abberline. The result was that Mary Kelly was murdered. The Doctor felt history change around them to acknowledge the new victim. An alternate timeline formed where Warner was the seventh canonical victim following "Amelia Marple" (Amy Pond). She was rescued but didn't live long after. (COMIC: Ripper's Curse)

Behind the scenes

 * Warner is not a historical figure. The unidentified fifth victim in the prose sources would have been intended to be the historical Mary Kelly.
 * Ripper's Curse only reveals which Mary was the victim after she was killed. Amy talked to both Marys without specifying who she was warning.