Guardian's Timeline Edit
She lost her parents after the Mayan virus spread over the world, and sought refuge in the subway tunnels of Old City. She was eventually found by Helen Magnus from the original timeline's past. However, at that time, she had already been infected with the virus and Magnus had to restrain her in the lab while trying to find a cure.
Eventually, time went by too fast for a cure to be found and Jessica transformed into one of the infected cannibalistic beasts, calling for the others to free her. Will Zimmerman then killed her with a gunshot.
Original Timeline Edit
Since the events Magnus witnesses under the influence of the Guardian occur around 2019, Jessica must already have been born in the original timeline and be a young girl in the year 2009.