Though she had to share a cover with her cousin if she appeared on one at all during this period, I thought this splash page came close to capturing the sense of what the cover for a Supergirl solo series might have looked like with her Supermanesque pose and generic setting.
Several "fantastic" touches of irony in this pic. 1. The texture of the monster is practically the same with that of Aunt Petunia's favorite nephew. 2. The monster name is used for Ma Grimm's bouncing baby boy! 3. Look at the 1st head on the left: remove the "hood ornaments" and this is virtually the same head for good ol' Uncle Benjy!