There are a pair of thigh-high boots that she used to use occasionally during the Silver/Bronze Ages, probably best-illustrated in Action Comics #402, “Supergirl vs. Superman.” This costume ...
But the upcoming Supergirl film seems to be based on one specific comic book, Tom King and Bilquis ... Woman of Tomorrow introduces Ruthye as a 14-year-old girl from a distant alien farming ...
As the trade explains, "In [the Supergirl: Woman of Tomorrow comic book], the bad guy is Krem of the Yellow Hill, who kills a young alien girl’s father. She draws Supergirl into the conflict.
Such as in Action Comics #1070 ... Amanda Waller is on trial, and Supergirl is off. Once she uses her new superpower on Power Girl. Looks like it. And there are other connections spilling out ...