In the span of Before Crisis and Crisis Core (the seven or so years duration before the beginning of Final Fantasy VII, as both titles' timelines overlap with each other's), Cissnei is affiliated with and works for Shinra as a member of the Turks. Although technically, the Turks is designated as the General Affairs and Investigative Department or as Vincent puts it when you find him sleeping in a coffin in the Shinra Mansion in FFVII, Shinra Manufacturing in Administrative Research, their members handle any sort of odd jobs the company throws at them, including but not limited to surveillance, reconnaissance, kidnapping, assassination, evidence destruction (to protect Shinra's image), cleaning up after SOLDIER, hacking and reprogramming computer systems, mail delivery to fugitives and so on.
Cissnei's presence is not very well-known even amongst the regular members of the Turks (and they had more than four members before the beginning of FFVII). As Reno commented to Rude while on an assignment to check for missing documents in the archive in the special Reno episode of Before Crisis, which occurred simultaneously as intruders appeared in the Shinra building in Chapter 4 of Crisis Core, new recruits of Turks do not even know that Cisseni exists8. This is due to the fact that Cissnei has been working for a different division of the Turks and has not had any interactions with her other colleagues seen in Before Crisis before appearing with Katana (Male) in Episode 18 of the game, which happened while Zack and Cloud were still captured as Hojo's subjects in Nibelheim.
After the Shinra building incident and ridding Sector 8 of Genesis Copies and malfunctioned security robots, Veld, the leader of Turks at the time, told Cissnei to keep an eye on Zack and keep track of his movements9, which she did throughout the course of Crisis Core, when she was not assigned to complete other missions.