(Cow TF) 'Grandpa...why?!'

Mary-Beth never liked going to Grandpas dairy farm. It was boring, dirty and smelly. The only fun thing to do on the farm was scaring the hell out of those dumb heifers.
As she made her way inside the cow shed for another round of spooking, she noticed the place was empty. "That's odd. They're usually here at this time. I guess Grandpa let 'em out early today."
Since her targets weren't there, she turned to leave but found Grandpa blocking the way. "Oh, hey Grandpa. I was just checking out the shed."
He said nothing as he approached her, staring at her with stern eyes. "Um...Gramps? You're uh...creeping me out here..." Mary-Beth said as she backed away from him, not noticing she was being backed into a pen until she fell in and her Grandpa had shut the gate.
"You've been spookin' mah girls, Mary-Beth." He finally said to her in a cold tone, "They don't like gettin' spooked n' I don't like it when mah girls are upset. Ya need to be punished, mah little cow."

Suddenly, Mary-Beth felt a sharp pain stab her nerves as she tried to get up, forcing her back down onto her hands and knees. The pain increased as her legs and arms started cramping up, the muscles thickening. Her hips pushed out along with her stomach and chest, muscle and fat thickening her body. She cried and moaned as her breasts disappeared from her chest, only for them to reappear between her changing legs and morphed into a large and heavy pink udder. As her neck thickened and stretched out, she tried to scream for help but all that came from her mouth was a pitiful 'moo'.
Mary-Beth could only look up at her Grandpa with her large, sad eyes, trying to beg him to make it stop but he only looked down at her in stern disappointment. All she could do now was wait for it to be over as she gave out another "Mooooo..."

Please note that I am not a writer but I wanted to write a story for this drawing.