Nothing is known of the very early life of the child that would be named Peachy Pet before she encountered John L. Thunder in the fall of 1941.  Kept at an orphanage with similarly aged children, she attended a local rodeo presentation with her class.  Johnny and his girlfriend Daisy Darling took pity on the children and with the surreptitious use of his Thunderbolt, induced a nearby candy vendor to supply the kids with treats.  In the rush to get them, a small girl – Peachy Pet – falls into the ring with a bull requiring rescue from Johnny.  Bonding with her, Johnny declares that he will adopt her and joins the rodeo as a star perfomer.  Aided by the Thunderbolt, Johnny wins every round and eventually, the regular rodeo performers begin to fear for the livelihood and stage accidents for Johnny that in turn are thwarted by the Thunderbolt.  Desperate, they decide to kill Johnny and when Peachy Pet overhears them, she throws herself at their mercy and pledges to tell Johnny their fears.  Moved, the performers stand down and Johnny abandons his rodeo career, going home with Peachy Pet (Flash Comics #21).

Peachy Pet proved a handful, willful and undisciplined.  She was in constant trouble in school (Flash Comics #22) and formed her own gang of misfits, with whom to get in more trouble (Flash Comics #24).  She accompanied Johnny everywhere including the Amazon (Flash Comics #27). In the summer of 1942, Johnny joined the Navy, leaving Peachy Pet with his parents.  Undeterred, Peachy Pet stowed away and after saving the ship became a mascot and good luck charm for the crew.  She stayed off and on the ship until Johnny was discharged nearly two years later (Flash Comics #53).  From there, she and Johnny spend several months in Hollywood trying to make it big but after several flops and rip-offs, found themselves back in the ancestral Thunder home (Flash Comiics #64). 

An interesting aspect of Peachy Pet is she periodically assumed control of the Thunderbolt (Flash Comics #22, 30) and engaged in a partnership with Shocko, the “son” of the Thunderbolt (Flash Comics #69).  Peachey could even summon Shocko with her own phrases “Sez me”.  She and Shocko engage in antics such as bringing home a horse (Flash Comics #71), turning Peachy’s birthday into a fiasco (Flash Comics #73), rescuing amnesiac Johnny from crooked scientists (Flash Comics #75) and even travel back in time (Flash Comics #80).  The extent of her relationship with the Thunderbolts are not clear.

In 1948, Peachy was approaching puberty and Johnny, losing control of the Thunderbolt, was lured back to Badhnesia (Superman #204).  Where Peachy Pet grew to adulthood and her fate after this point on Earth-Two is unknown.