So near as I can tell Applejack started off as a villian from a former comic line. She was a Jack the Ripper copycat. Using the name Nathan East as opportunity to gain revenge on those who had made fun of her, especially ponies.

In a later story line it was reveled her craziness was because of a evil ice cream flavor that forced her to do murders. Made by Catrina a sorceress with the ability to shoot lightning from her eyes, and the ability to control snow and wind and ice which Catrina gave to Scorpan to force apon applejack. Who was later taken down by Megan Williams during 'Rescue from Midnight Castle', Applejack then teamed up with Ms. Williams for further crime fighting adventures.