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 her father was killed while fighting Cobalt Blue. He had managed to kill his enemy but was not prepared for the next host appearing only minutes later. Sela then emerged as a conscious manifestation of the Speed Force itself.