One of the three top Tiberium scientist, Dr. Elena Petrova works for GDI together with Dr. Ignatio Mobius and his daughter, Sydney, researching Tiberium and its practical applications.
At the beginning of Renegade, she was captured by the Black Hand in Guatemala along with the Mobiuses and was forced to work on practical methods of human augmentation with Tiberium.
While it is unknown exactly when she changed her loyalties, she switches sides during her work with Mobius and defects to Nod, likely because of the indoctrination that the scientists went through during their 'visit' with Nod. After she had been trusted by Kane, she takes the position of main researcher in the genetic enhancement program "Project ReGenesis". Her experience in Tiberium research allows the Brotherhood to perfect the process and results in creation of super soldiers using controlled Tiberium infusions. Petrova eventually undergoes the process herself, resulting in the creation of an entity Nod considers a being closest to perfection.
Petrova is available in multiplayer, on servers with the extras variable enabled . To access her, one needs to hold ALT while selecting the characters menu. Petrova is equipped with the standard pistol and Volt Auto Rifle and is available in two flavours: regular for GDI and mutated for Nod.
Note: Oddly, her Tiberium-mutated form cannot heal in Tiberium. In addition, while in singleplayer she can cloak much like Black Hand stealth soldiers, she cannot in multiplayer.