Millie Foss is the daughter of the late Digsy Foss and his late husband in Barry Allen and Kara Danvers' dream movie musical world that was conjured by the Music Meister. She resembles Iris West. She was in love with Tommy Moran who was Mon-El's counterpart though their love was forbidden due to their parents being rival gangsters. She ceased to be when Barry and Kara were freed from the dream world by the real Iris and Mon-El.
Millie Foss secretly got into a relationship with Tommy Moran, the son of Cutter Moran. She snuck into Cutter's club where she spent time with Cutter. When Barry Allen and Kara Danvers arrived and told her that her father is worried, she refused to return home, calling Tommy Moran her home. But, with a little more persuasion, Millie and Tommy agreed that she would go home and they would both tell their parents the truth. When she made the revelation to her parents, they were distraught. However, they seemingly accepted her relationship by singing "More I Cannot Wish You".