Peachy Pet was introduced into the Johnny Thunder storylines as his adopted daughter, part of a bratty-child-and-clueless-parent slapstick humor trope that was popular at the time. Most of the slapstick humor centered on her gleeful love of violence, on her tough kid wisecracks, on the general chaos she wrought around her, and on her talent for shifting all the blame for her antics onto poor Johnny while taking all the credit for Johnny Thunder's acts of heroism. Throughout the strip, Johnny remained helplessly unable to handle her or to stave off her ill-tempered contempt for him, though Johnny clearly cared deeply about his adopted daughter and she clearly cared deeply about her adopted father.
The character came close to replacing Johnny in his own strip.
Peachy Pet is a bratty little girl, complete with stereotypical blonde curls, who seems to have been adopted by Johnny Thunder. Tastes in slapstick humor change, so Peachy Pet's joyful cruelty has not aged well, and like many Golden Age sidekicks, Peachy Pet has been left to dwindle to obscurity over the decades since then.