Once upon a (rewritten) time...
Celestia had the idea to create a rock garden. To create and maintain it, she hired the Pie family. Worst Idea Ever. (Well, no. That would be "Ignoring your sister's problems". But this would be in the top 10)
Some of Little Nimrod's Adventures in Canterlot would achieve the status of legends. On her first day in the castle, she was exploring with her sister Maud but what to their wondering eyes should appear? It was Celestia's butt -a not so miniature rear.
Pinkie had been driving everyone crazy by asking everypony she met "What do you do here?". When she asked Celestia, Maud told her "Pinkie, can't you see that she is MUCH too important to actually do things? She just tells other ponies to do things."
Pinky replied "She got to be the boss because she's the biggest! She sat on all the others and SQUISHED them with her butt!" Then she asked Celestia "If I eat tons of cake can I get to be as big as you?"
Maud said "Don't be silly, Pinkie. There isn't that much cake in the world."
At that point, the guards caught up, and the two fillies fled. On her way out, Pinkie pronked onto Celestia's head, slid down her mane and launched herself off Celestia's backside. They fled down a corridor, followed closely by several Guards and Celestia, who Wanted A Word With You, Pinkamena Diane Pie (actually, "Where are your parents?" were to be the first of many words).
They broke into the exam room just before Dash pulled off the first Rainboom. Pinkie's Pinkie Sense correctly predicted a doozy. In the ensuing confusion, Pinkie was impressed enough by magic to get a star Cutie Mark. Twilight got a lightning bolt for blasting things. Spike imprinted on Pinkie. So, Spike was raised by Pinkie. Pinkie and Twilight became friends and were both taken as Celestia's students.
The others got their Cutie Marks the way they always did.
Fluttershy was trying to fly when she fell to what was almost her death. She was saved by butterflies and got a butterfly Cutie Mark by comforting the animals after the Rainboom
Dash made the Rainboom hurrying home and got her apple Cutie Mark when she got back home to Sweet Apple Acres
AJ got her diamond Cutie Mark by helping her younger sister Rarity when she needed it & realized that she liked helping folks and finding the hidden good in Ponies and things
Rarity got her balloon Cutie Mark at the cast party after the play when she realized parties, plays, whatever she loved making Ponies happy
Eleven Years Later...
They were looking for The Elements of Harmony. The Great Detective Pinkie said "I deduce that they are in the basement of the abandoned house next door!"
Her bumbling (but Loyal) assistant Twilight said "Don't be ridiculous, Pinkie! There is no abandoned house next door!" Twilight's habit of constantly using facts and logic to contradict her friends was one of the many reasons that she had very few friends.
Pinkie said "Then we'll BUILD a house next door!"
Thus, the Elements were located, Nightmare Moon was defeated by having to listen to Twilight describe a Candlelight Supper & Mayor Mare escaped to found Equestria.
Pinkie the Wise would assign the Elements as follows
Rarity became The Element of Good Cheer for inviting total strangers to her elegant Candlelight Suppers (taught to her by her Canterlot friend Hyacinth Boquete (pronounced Bucket) ) & how happy everybody was to escape from Rarity's Elegant Candlelight Supper
Rainbow Dash became The Element of Honesty for calling Rarity's Candlelight Suppers "A nightmare forged in Tartarus and inflicted on Equestria because Paradise wouldn't have them and Tartarus couldn't hold them"
Twilight became The Element of Loyalty because she stayed with her friend through the horrors of a Candlelight Supper
Fluttershy became The Element of Kindness for helping two strangers escape from a Candlelight Supper
Apple Jack became The Element of Generosity for giving shelter to those fleeing an elegant Candlelight Supper
History does not record Rarity's response to Pinkie's comment that "It was either go into the Everfree or back to The Candlelight Supper. We took the soft option." This one of many good things about that night.
A year later, some fool accidently sent Starswhirl's book to Twilight and let Derpy deliver it. (She still doesn't know what went wrong. I'd say the answer is "Plenty!")