First of all: These are the human versions of Rarity and Applejack, so my headcanons may be different than yours and I'm sorry if they weren't described entirely.
Secondly: This is my first time writing about any of the ponies, so I apologize that it's not only short, but probably a bit out of character. I really tried my best on this one, and I hope it's enjoyed.
"Oh Applejack, do try to stand still!"
"I'm tryin! I been standin' for a while though! Couldn't ya have gotten someone else to do this?"
A dark hand went up to Rarity's forehead and wiped a tiny bead of sweat off of it. She shuddered internally. The moment she was done, she was going to take a nice, long, relaxing bath.
For now, though, she had other things to do. She stuck another pin into the dress, just barely missing the sun tanned skin of Applejack's arm, to mark where she wanted to put more lace.
"I absolutely cannot! Come now, dear," she placed a well-manicured finger under Applejack's chin and tilted her head up. Applejack found herself staring in the mirror before her.
She watched through the mirror as Rarity's slim figure moved behind her. She watched Rarity's fine, but slightly bony, hands run themselves down along Applejack's figure, "Just look at you! This dress was made for someone not just of your figure, but of every detail of your appearance as well! I simply can't ask anyone else to help me when you're the one who shall bring out its full potential!"
Applejack found herself squirming and blushing from the attention that was brought to her appearance.
Rarity had pulled her long, messy blond hair into a high, neat ponytail. She'd managed to convince Applejack into a very elegant, green gown to assist her for what she called "a short while." At the waist, the gown went outward, just like the gowns that she'd seen the princesses wear all the times they visited Ponyville before. The sleeves fit snuggly around her arms and stopped at the elbows. There wasn't much detail on the dress just yet, but pins stuck out all over indicating where the seamstress wanted to add things to it.
A sigh came from Applejack's mouth, and she turned her eyes to the Rarity in the mirror. "Look, sugarcube. I'm real honored and all that you think all that 'bout me, but a dress this fancy and well made by ya would look great on anyone."
She watched Rarity pull her purple lips into a pout. A moment later, the real Rarity moved in front of her, "Oh, but Applejack! I already know that it'll look good on anyone, but it looks absolutely divine on you!"
The manicured right hand of Rarity's was placed onto Applejack's cheek, "Oh please, love! You've just got to be the one to do this for me!"
The seamstress watched Applejack's eyes roll in her head, then let out a squeal of delight when the farmer girl nodded her head, "Only 'cause it's you."
"Oh you absolutely will not regret this!"
With a soft giggle, Applejack closed her eyes and found herself listening to the familiar sound of the heels Rarity wore clacking about on the floor."
A moment later, she could feel soft hands on the back of her neck. It took her another moment more to recognized that Rarity had taken off her necklace.
Her eyes opened quickly and she turned around, despite having been told not to move. She felt pins poke her in various places as the gown swished on the floor.
"Please, give it back, Rarity! It was given to me by…" Her voice trailed off for a just a moment before she picked up where she left off, "You know it's important to me!"
Rarity gave a soft smile to reassure Applejack and kissed her forehead. "I just want to see how a choker would match the gown. I promise your necklace is in a safe place."
Applejack noticed Rarity slowly turning something between her fingers, just above her chest. She caught glimpse of an apple and noticed the chain around Rarity's neck that had not been there earlier.
She sighed and gave a nod to Rarity to let her know that she trusted her, "So, what's a choker?"
The taller of the two clapped her hands together, "It's a bit like a necklace, but it fits around the circumference of your neck instead of resting further down near your chest."
Applejack gave a nervous smile, and Rarity placed her hand upon her shoulder, "You needn't worry! I can assure you that it has nothing to do with choking you."
She turned Applejack back around and began trying different ribbons and laces of different shades of green, brown, and red against Applejack's neck. She had to figure out which would match the gown best or if she ought not to use one at all.
She, in the end, settled on a shiny brown ribbon of a lighter shade and darker green lace to put on the top and bottom edges of it.
She walked circles around Applejack for a few minutes, studying the pins, their locations, and the different colors on the end that she used to mark what change or addition was to be made. Soon, she smiled with satisfaction, "We're all done! For now, anyways. I want to apply the changes to the dress and then try it on you once again."
Applejack breathed out a sigh of relief, "Phew! I'm gonna have to go for a run after this! My legs an' arms are all stiff."
Rarity helped Applejack out of the gown first. Applejack then got herself into her comfortable clothes again: simple jeans that had dirt stains in many places, cowboy boots, and a button up orange plaid shirt. A look, Rarity had decided long ago, that only Applejack was able to pull off.
She watched as Applejack took the ponytail down and simply tied it off near the end of her hair.
Rarity then stepped in and put Applejack's necklace on for her. She kissed both of her cheeks, "Thank you so much for helping me, my dear!"
Applejack managed to force down her blush, "Don't worry 'bout it, sugarcube. Just lemme now when ya need my help again. I'll come on over in a heartbeat."
Rarity led Applejack out the door and watched her until she was out of sight. She went upstairs and started the bath, eager to relax.
While she waited for the tub to fill with water and bubbles, she got the items she needed for her face mask. When the tub still hadn't filled up, she brushed Opalescence. Once the tub was full, she put the face mask on and laid down in it.
There she stayed for a while, thinking about her plans for the dress and how lovely Applejack had looked in it.