Miss Hart was the headmistress of the Midvale Orphanage as of 1959. She was a kind woman, and cared for the children at the orphanage, including young Linda Lee. ("The Supergirl from Krypton", "The Secret of the Super-Orphan!")
She shared a close bond with Linda Lee, and felt sad when she was temporarily adopted. When Supergirl later returned to the orphanage, the two shared a happy reunion. ("Supergirl's Fortress of Solitude!")