Author's Note
By the way, I'm Sunset Shimmer. Only difference is that it was at my house. I seriously cleaned the floor but failed. 
My friends are very emotional, even if it's something as small as whipped cream.
OK, Maybe A Little...
"Too bad Rarity isn't here." Sunset Shimmer thought aloud as Pinkie Pie stroked a brush through her hair. At the same time, Sunset was putting Fluttershy's into one long braid down the middle.
"I'm sure she's having a lot more fun at that fashion show." Fluttershy commented.
"Um, I think I just messed up." Pinkie said nervously, staring at Sunset's hair.
Sunset looked up from her work at the mirror, and went wide-eyed. "Pinkie...How...?" Sunset's hair had poofed up, almost as much as Pinkie Pie's. If it wasn't for the color differences, you could almost mistake her for her friend.
"It was an accident! I was just brushing it and then it all went 'Poof'!" Pinkie defended.
"You have the magic touch!" Sunset giggled. "I can't even make it do that! Anyway, it's fine. I can redo it later."
"Now what?" Fluttershy asked, moving her braid so it rested on her right shoulder.
"Cupcakes!" Pinkie exclaimed, dragging them both into the kitchen. Almost everything you could think of was on a counter...except for cupcakes. Noticing the look of confusion on their faces, she added, "We're going to bake them, sillies!"
Sunset picked up a tube of frosting. "This sounds fun and all, but I can't bake," she admitted.
"Don't worry, once I show you, it'll be a piece of cake." Pinkie said. "Or a 'cup cake'."
An hour later...
"Quick, get water!" Pinkie exclaimed, running out of the kitchen with Sunset on her heels, the both of them covering their ears from the blaring fire alarm. Fluttershy grabbed a bowl and put it under the sink, then hurriedly passed it to Pinkie, who splashed it over the oven to put out the fire.
The alarm faded, and the smoke gradually cleared once Sunset opened a door. "I thought you said you had it under control!" Sunset exploded.
"Oops..." Pinkie shrugged a shoulder nervously. "Maybe baking should wait until the next sleepover."
"No!" Fluttershy and Sunset shouted together, then doubled over laughing.
"You have to admit, almost burning the house down was pretty fun." Sunset smiled.
"You should have seen your face, Pinkie." Fluttershy joked. "So, what should we do next. It's getting kind of late."
"Awe, come on, Fluttershy! Where's your sleepover spirit?!" Pinkie asked. "Who's ready to do some dancing and pillow fighting?!"
"Me!" Sunset ran to Pinkie's room. "I'm going to get my pajamas on, though." She disappeared into the room.
"Let's go set up Just Dance!" Pinkie Pie waved Fluttershy to follow her to the living room and over to the TV where the PS4 was connected. Flutters handed Pinkie a disc which she slid into the slot just as Sunset came down the stairs.
"I call first pick!" Pinkie exclaimed. "The Smile Song!"
"That one's hard-" Sunset was cut off.
"Who's sleepover is this?" Sunset rolled her eyes.
After the song was over, Pinkie Pie jumped up, exclaiming her victory. Of course she won.
"Be right back!" she suddenly said, zooming up the stairs to a room invisible to Fluttershy and Sunset. They both shared a look before a pillow slammed into the back of Fluttershy's head.
"Ow." she sighed, rubbing the spot it had hit her. Pinkie was behind them, hidden behind a wall of pillows, projecting them in random directions from time to time.
"Where in the world did you get all those pillows?" Sunset wondered.
"Maud's room!" The pillow fort shouted before a pillow hit Sunset in the face.
"Hey! Let me and Fluttershy play!" She grabbed Fluttershy's hand and took an arm full of pillows from the fort, then setting them in a corner before hiding behind the wall. Fluttershy stood in the middle of the room, unsure on what to do.
"Fire!" Pinkie exclaimed and threw pillow after pillow at Sunset, some occasionally hitting Fluttershy. Sunset did the same.
"Um, girls. I'm not sure I like this game very much." The girl in the middle whispered as she dodged lightning-speed throws.
"Hold fire!" Sunset stopped throwing, and then so did Pinkie. "I'm sorry, Fluttershy. We didn't know you weren't having fun. We can do something else now."
"Well, I did bring my Littlest Pet Shops..." Fluttershy played with her hair. Sunset nodded yes and they went to go get them.
"This is so boring!" Pinkie said later, wobbling a cat's head around in a dollhouse. Sunset nudged her, hinting that she was being rude.
Fluttershy yawned. "Is anyone else tired?" Pinkie's hand shot up and Sunset pulled it back down. "I think I'll go to sleep now. Goodnight, girls." She set up her sleeping bag on the floor and snuggled into it, quickly falling asleep.
"Ugh, FINALLY!" Pinkie threw down the cat and stood up. "I don't know how much more of that I could take!"
"Well, we can't always do what you want. You have to give everyone a chance to have fun." Sunset commented, glaring at her.
"Ok, ok. What do you want to do."
"I'm actually a little tired now, I think I'll set up my stuff and read?" Sunset got up to get her sleeping bag and book out of her backpack.
"You, too?! But I'm not tired! Come on, I have an idea of what to do!"
Pinkie dashed upstairs. Sunset followed her, curious. Her energetic friend opened the fridge to find it full of whipped cream. She grabbed some, then turned to Sunset, who gave her a confused look before trailing behind her downstairs.
Pinkie Pie knelt down next to Fluttershy and uncapped the whipped cream. "What are you-"
"Shhh." Pinkie shushed, turning back to what she was doing. Flutters was lying facing the ceiling, and Pinkie put whipped cream on her face just under her nose, making it look like she had a mustache. Pinkie giggled as her victim turned around on her side.
"Pinkie Pie, stop it! You're going to wake her up!"
"Wanna try? Come on, it's fun!" Sunset shook her head. Pinkie attempted to do a second string of cream, but Fluttershy sat upright and wiped at her nose, half asleep. Until she noticed there was whipped cream on her face, then she turned to see Pinkie hiding the can behind her back and Sunset shrugging nervously in the background.
"W-what are you guys doing?" she wondered tiredly. "Did you put this on my face?"
"Um, the floors covered in whipped cream. I...think I'll go get a sponge." Sunset Shimmer slipped upstairs, not wanting to be apart of this.
Fluttershy turned to Pinkie. "We only did it for fun. We were going to clean it up, promise," she defended.
"'We'? Was Sunset in on this, too?"
"No, I was about to go to bed. Pinkie has full responsibility." Sunset explained, putting the water bucket down and scrubbing the floor with her sponge, occasionally squeezing it into the bucket.
Fluttershy got up to move to the couch at the far end of the room, and Pinkie sat at the other one, back to the both of them.
A few minutes later, Sunset went over to sit next to Fluttershy. She was wrapped in a blanket, shivering.
"Why'd you let her do it?"
"Huh? Oh, no, I didn't. I mean, I tried to tell her not to, but..." Sunset fell silent. "Sorry, Fluttershy."
"Now I don't want to go back to sleep. I'm afraid you guys'll do it again."
"I'm sure she won't. It was just a harmless joke." Sunset put her hand on her friend's shoulder, but she shrugged it off. "Why don't you go talk to her?"
"No, I want her to apologize first. If you want to help, go tell her that." Fluttershy scowled.
Sunset sighed, but went over to sit with Pinkie Pie. "Go away," she said, crying a little.
"Ok, ok. Fluttershy just wanted to say she was sorry." Sunset lied.
Pinkie sniffled. "She did?"
"Yes, she didn't mean to make you so upset. But she does want you to say sorry to her, too."
Pinkie's eyes narrowed. "Forget it. Tell her she has to apologize in person, first."
Sunset frowned. Would they just get over it already? This was supposed to be a fun sleepover.
Then she had an idea. Halfway to the other couch, she said, "So, I'm the messenger now?" She giggled, trying to get her friends to do the same, but they just seemed to ignore her.
"In the game we're playing, I mean." Sunset continued with a hopeful smile. Fluttershy and Pinkie Pie looked up.
"Game?" Fluttershy asked.
"Yeah. You know, the one where you two are sisters and are very close, but you got into a fight and won't talk to each other. I have to find a way to get you back together."
Pinkie laughed. "I've never heard of that game. Did you come up with that just now?" Sunset nodded. "I wanna play!"
"You already are. Both of you!" Sunset giggled. Her plan was working. She looked over to Fluttershy, who was starting to fall asleep. "Maybe we should postpone until tomorrow, though."
The both of them lied down and went to sleep.
The next morning, Sunset and Pinkie waved goodbye to Fluttershy. Before Sunset left, Pinkie pulled her in for a hug. "Sorry about last night. Thanks for helping out."
"It's no problem. I'm just glad you two aren't very stubborn." Sunset waved as she hopped down the porch steps. She really was doing a good job at fitting in.
