Sela Allen was a Flash active in the 23rd century. Her father was her predecessor. In 2231, the Cobalt Blue who was rival to her father managed to capture all three of the Allen Family. He crippled Sela and killed her mother while the father of the family was forced to watch. Cobalt Blue then turned his attention to her brain. By the time the Flash got free, Sela was damaged beyond repair. In desperation he took the girl to the Speed Force, hoping it would heal her.
Eight months later when her father was killed by a new Cobalt Blue, Sela appeared as a conscious manifestation of the Speed Force, projecting a humanoid appearance and able to lend speed to other objects but unable to physically interact with the world.