Like the Amish in real life, once an "Amish" pony reaches a certain age (or gets her cutie mark), she leaves home and experiences the world, then decides wheter or not she wishes to return. Though her parents tried to understand her, they jsut couldn't, and she was cut off even more. Pinkie didn't just look different, however, as she didn't totally understand her family's faith.
However, she was deeply devoted to her family, and this is where she developed the "big sister" mentality, which is how she treats Fluttershy. She was the oldest of the three, and just didn't fit in. Pinkie was always different from her family and her sisters, Inky and Blinky. She may have also been adopted to make sure the Pies had a child, though I find this unlikely. She may have been a "throwback" to an older relative who was pink (or simialrly colored) and fun-loving. Pinkie Pie was born on the rock farm to a family that is the pony equivalent of the Amish. However, for the purposes of this WMG, I am assuming everything she has told us is at least mostly true (though she's an Unreliable Narrator). Pinkie Pie's Backstory.We don't know much about Pinkie Pie's backstory. Being created by Discord also explains Pinkie's reality-warping tendencies. However, Pinkie's family escaped and made a living for themselves by working on a rock farm. Adding to my original WMG, Pinkie Pie is immortal because Discord created immortal ponies in hopes of torturing them for all eternity.well, Pinkie Pie, she slipped up at the end of her story and said, "And that's how Equestria was made!" When telling her story to the Cutie Mark Crusaders, she neither wanted to reveal her secret immortality nor be any more different from her friends, she told them that what inspired her was the Sonic Rainboom. She decided that from then on, she would spread her newly found joy to everyone she met. However, one day, while she was working outside, Pinkie Pie saw the defeat of Discord, and realized joy, earning her Cutie Mark. Pinkie Pie is immortal, and her Cutie Mark story is, in a way, how Equestria was made.Pinkie lived on a rock farm with her family during Discord's rule, and they were all consumed by despair.