Courtney Whitmore/Earth-90

Courtney Whitmore is a fictional minor character featured in the DC Television Universe. She made a small cameo appearance in the "What's Past Is Prologue" episode of The Flash in 2018. She was played by an unknown extra.

Biography
Courtney Whitmore was a blond-haired girl who became a costumed adventurer known as Stargirl. She hailed from an alternate reality known as Earth-90. Her prone body was seen lying face down on a battlefield in the presence of a Monitor named Mar Novu. The Flash of that world managed to escape from whatever fate befell Courtney.