So I decided to write a little thing to go along with this. I guess.

It was the day before Nightmare Night. Trixie was scheduled to do a performance up in Canterlot, and Sprite decided to tag along for the ride. It was Nightmare Night, and she hadn't seen Princess Luna in some time, so it was the perfect opportunity to take a trip up there.
The two of them wanted to get to Canterlot ahead of everyone else, so they had their things packed and gathered for that day. By sundown, they were well on their way on the dirt path to the large, fancy city. Sprite, having been taught to "potty before leaving," was more than prepared before and during the trip. Trixie, however, seemed to have been too busy to take a potty break.

The whole way to Canterlot, Trixie fidgeted and squirmed where she sat. Every bump in the road was agony for her. Once or twice she had let out a soft groan that caught her fluffily suited marefriend's attention.
"Are you okay, Trix?" Sprite asked, tilting her head.
Trixie hid behind her mane some. "T-Trixie is fine! Everything is fine." She managed to keep herself still long enough to some-what convince Sprite.
The Alicorn merely shrugged some. "It looks and sounds like you gotta potty, but okay!"

Halfway through the trip, Trixie was almost to her limit. Her body was practically screaming for her to get some release, but the unicorn fought the urges back time after time. One large bump, however, was her tipping point.
THUMP
Trixie and Sprite both landed hard on the stage coach's floor, one with a soft crinkle. Trixie let out a soft gasp as she felt some pee push out of her and onto the floor.
With a soft whine, she quietly looked at the suited Sprite in front of her. She returned her look with one of concern.
"Are ya one-hundred percent sure yer okay, hun? Ya look mighty... Err..." She paused to blush some, trying to think of a good way to put the situation.
Trixie just looked down at the floor, a blush rushing across her face. "I... I REALLY need to go..."
Sprite's ears perked up inside of the Discord-themed outfit. "What was that?"
Trixie jammed her eyes shut as she fought off another wave of desperation.
"I said that I REALLY need to go!" The magician mare looked up at Sprite with a thick blush.
Sprite dug through her bags and took out a fresh white and pink diaper.
"You wansh wan of deshe?" Sprite asked from behind her diaper-filled mouth, grinning all the while.
Trixie felt even more embarrassed as she gritted her teeth and began to scowl some. "I... You know I don't need them!"
Sprite giggled some as Trixie paused.
"...But I would request one.. P-please..."