design notes:
-she BIG
-clydesdale/draft horse shape and face shape
-wears granny smith's scarf after she passes away
-dappling pattern bigger on butt and shoulders
-larger front hooves
-rainbow power gave her pink and red streaks in her mane.
-she has granny smith's old shawl and bright macintosh's hat - all of the apple family has a tradition of passing on clothing items when they pass away. wills mainly consist of "give this pony my special hat/earring/bow" and "this pony is in charge of my orchard now."

applejack doesn't have much character development because she's already great! she's just doing her own thing living her life like a girlboss. she starts out very stubborn and learns to depend on others (and learns a little bit of tact) over the course of her friendship with others. she's the perfect earth pony mare, big and strong. the apples are some top tier earth ponies, and have especially strong growing magic that keeps the soil they walk on fertile and their trees healthy. applejack is strong as hell and only gets buffer as the series goes on. she kicked an entire huge boulder out of the way of ponies in shadow play part 1.
"dear princess celestia .... I DIDN'T LEARN A THING! I was right all along!"