In FFVII:BC, the generic Turks that the player controls are named by the player whatever they wish, but are simply identified as default by whatever weapon they prefer to wield – Cissnei is known ‘Shuriken’ for obvious reasons.
The reference in FFVII: Crisis Core gives a little more information on this, in that she tells Zack that she was actually raised by the Shinra and that she doesn’t know who her parents are or even what her real name is.
Basically, Cissnei doesn’t have a real name.