They wont't stop filling (STORY)

 It was late, and Sarah was beyond bored. They came to the party a few hours ago, but nothing really exciting had happened since then. She was with her friend Alyx, who were drunk as a towns fool. Sarah didn’t drink, and she was beginning to suspect that it was the reason why she was bored.
“I think I’ll head home“, she eventually said and stood up from her chair.
“No way, Sarah. You can’t ditch me, we’re staying here”. Alyx grabbed her arm and dragged her back into her seat.
“I’ll get you a drink, I promise it will help you”.
“No way, you know I don’t drink”, Sarah replied.
“Yeah I know, but trust me. It’ll be alright!” She got up from her seat and turned towards the kitchen.
“Alyx wait, I’ll get one myself. Feel like stretching my legs a bit”.
“Oh, ok. My bag is the one with the red label okay? Just don’t mix it too strong”.
She wouldn't. She didn’t even plan to get a drink. However, Sarah was a bit thirsty though, and wondered if they had something refreshing in the fridge.
The kitchen was empty, all the others were in the living room playing some random drinking game. Sarah opened the fridge, only to be disappointed. It was stacked full of beer, alcoholic soft drinks and some soda. She didn’t really feel like drinking anything sweet since she’s been sipping on coke the entire evening. Then she saw a milk bottle in the corner. This will do, she thought.
She grabbed a cup, filled it and started walking back to the rest of the group. She passed a girl in the doorway that she had not seen before. Her outfit and hair was almost completely black, arms covered in tattoos and a piercing in one of her eyebrows.
“Hey Sarah, mind grabbing a beer from my bag while you’re there?”, Alyx yelled from her seat. Sarah imitatively turned around, only to bump into the girl who she recently passed. She dropped her cup with milk, spilling it all over the stranger.
“Fuck!” The girl yelled.
“Oh shit, I’m so sorry”, Sarah apologized. “I didn’t see you...I’ll get...”
“What the fuck is this? Milk? Did you really spill milk all over me? I’m gonna smell so bad now”, she girl interrupted. Sarah could tell that she was upset.
“I’ll get a tissue, there should be one by the…” Sara started.
“And who drinks milk at a party anyways?” she yelled.
“Well I di”...
“You fucking dumb cow” the girl said.
Sarah didn’t know what to say. She stood in front of the girl, speechless.
“Just get the fuck away, I’ll manage on my own the girl said.
Sara turned around. That was it, she was leaving the party. She started walking towards the door.
“Hey you...cow!” The girl yelled from the kitchen door.
Sarah turned around.
“Don’t worry about your milk. You’ll get plenty more soon”, the girl smiled and walked back to the kitchen. What did she mean by that?
Sara ignored her, and went outside.
It was pretty warm, so she didn’t need a jacket. Her house was a 20 minute walk away, but she would cut the time by half if she walked through the woods.
She followed a small path next to a small river. The moon was full, and would sometimes shine through the tree branches. After some time walking, she felt a bit strange. She couldn’t quite figure out if she felt good or bad, it was a strange feeling. Her breaths started to increase, and her fingers started to tingle. She stopped, and looked down at her hands. There was something odd about them, they felt stiff, and a bit hard to control the movement. All of a sudden her nails felt really cold, and they started to get darker.
“Wait, what is going on?”
Then her ears started to get warm. She grabbed them, and she could feel them stretching and growing longer in her hands.
The confused girl grabbed her phone so she could inspect herself, but when the light from the screen hit her fingers she screamed, and dropped her phone. Her hands were darker, she rubbed them and realized they were covered in a soft layer of hair.
“No no no, this can't be happening”.
Her hands started to shrink a bit, and her fingers started to fuse together at some places. Slowly, they were changing into hooves. It didn’t feel bad though, quite the opposite. Like the lovely feeling when someone were caressing her hands.
Then her nipples started to stiffen. She locked down, and she could clearly see them poking through her top. Her breaths got heavier, and with each breath she felt a tingling, pleasurable wave hit her, from head to toe. Her breasts started to get warm. She grabbed them, but quickly removed her hands, or hooves, when a pleasurable, arousing feeling flooded her body, starting from her chest.  
“Oh, god, they’re really sensitive”. She moaned.
Then they started to grow. Slowly, her tits were swelling larger and larger in front of her eyes. She felt her skin stretching.
“Ahhh, what’s happening to mooee”? She moaned in pleasure. It felt good. Arousal were building inside her. She started to get an impressive cleavage, and her nipples had grown even bigger. There was a strange sound coming from her tits, like they were filling up with some kind of liquid.
At the same time, her toes had gone through the same changes as her hands. Her ears had grown longer and floppier. She felt two bumps on her forehead, slowly growing. She reached for them to examine.
“Hoooorns?, she moaned.
As her breasts were expanding, she felt better and better. It was almost orgasmic. She was breathing heavy. like she’d just ran a marathon. With each breath came more pleasure.
She felt her thighs thicken, and her pants were getting tight. She tried to look behind her, and she saw her small butt was beginning to grow bigger as well. It swelled big enough to be called a proper bubble butt, but the growing didn’t seem to stop.
Her pants started to tear, flesh poking out from the holes. Then she felt her tailbone stretching, growing longer. A small tail ripped through her pants, and grew longer by the second.
“A tail?, oh my goood. I’m tooourning into soooome kind of animoool!, she moaned, almost mooed like a cow.  
She started to grow hair all over her body. White on some places, brown on the rest. Her horns hair grown fully out, and her nose had transformed into something not human like.
“Sooomebooody help moooo”, she tried to scream, but it came out like a mixture of a moan and a moo.
Her breasts started to accelerate the growth. They were filling up, getting round and juicy.
As they grew, so did her arousal and pleasure. Her shirt could hold her right tit any more, so it bounced free. She grabbed it with her hoove, and an explosion of ecstasy rocked through her body. Milk shot outwars from her tits, spilling in all directions.
“Oh myyy gooood, I’m gooona...I’m gonna…
She started to shake. Her pussy was wet and swollen. She pulled her hair with her other hoove. I’m goona cum! She screamed. And as she came, more milk exploded from her tits. Her boobs didn’t seem to stop growing either. They kept growing and growing, turning a bit pink.
The girl stood there in the forest, experiencing orgasm after orgasm. It didn’t seem to stop ether. She came, over and over again.
“Ohh, mooyy gooood! She moaned.