Jerry Coleman (birth/death dates unknown) wrote nearly 100 stories for DC Comics, beginning with Mystery in Space #3. By the mid-1950s he regularly scripted for Weisenger's Superman titles. Among Coleman's best-loved Super-tales: "Superboy's Last Day in Smallville" (Superman #97) and "The girl in Superman's Past" (Showcase #9).
Brainiac exposes Superman to a combination of Red and Green Kryptonite to see what kind of reaction it will create. Supergirl makes a brief cameo.
"Ma and Pa Kent Adopt Supergirl"
Supergirl falls asleep and dreams what if she was the first Kryptonian child to arrive on Earth, and it was her who was discovered and adopted by the Kent’s instead of her cousin, Superman.
*I am reading one Supergirl aka Kara Zor-El (Earth-One) story every day, starting with her introduction in May 1959 in Action Comics #252, until her final appearance in October 1985, in Crisis on Infinite Earths #7.