Not-Sasha was presumably created by the table first observed in the case regarding Graham Folger (MAG 3). The table in question was delivered to the Institute (MAG 35) and was moved into artifact storage. Sasha took refuge from Jane Prentiss's attack in that room, where she encountered an unknown figure. Not-Sasha can be heard for the first time after that, repeating the last words spoken by Sasha. (MAG 39).
Not-Sasha was debriefed by Jonathan Sims following Prentiss's attack, and Sims did not notice any changes when talking to Not-Sasha, other than noting she seemed to be showing signs of stress from the attack. Not-Sasha claimed that Sasha's recording during the attack was lost, and the other recordings on which Sasha's voice can be heard also disappeared following the attack (MAG 40).
Following the statement made by Helen Richardson regarding the appearance of Michael, Sims asked Not-Sasha about "her" previous statement regarding Michael, noting that it had been lost following the appearance. Not-Sasha was evasive about re-recording her statement, and after she left Michael appeared and warned Sims that she was lying to him. (MAG 47)
Sims stumbled across Not-Sasha staring at the table later, where she described its pattern as a web instead of a fractal, and noted that the table may have caught all of them. (MAG 51) Following this encounter, Sims discovered that she has been spending time at Madame Toussard's Wax Museum every two or three days. When confronted about this, Not-Sasha claimed that she had a new boyfriend she liked to have lunch around there. (MAG 52)
Not-Sasha caught Sims going through her desk, looking for anything unusual. He claimed he was looking for the files on the Hill Top Road case; she reminded him of her request he not record her private conversations. Sims noted that photos of Not-Sasha and her boyfriend Tom looked suspiciously like stock photos. (MAG 57)