this reminds me of something but i cant put my finger on it…

“Standing by the stove, watching the sun come up as she prepared breakfast, Applejack’s ears perked up as she heard Applebloom make her way downstairs. Though she’d grown accustomed to her sisters… differences… her uncoordinated hoofbeats and the sound of bone clicking against bone still made her wince.  
“G’mornin Applebloom! You sleep okay?”  
Applejack knew very well that in her current “condition,” her sister didn’t sleep, but the Apple family were ponies of habit, and asking the old question each morning helped bring a tiny feeling or normalcy to Sweet Apple Acres.  
“Ah slept well enough! No nightmares!”  
Applebloom responded, her voice a soft rasp caught in the throat. Applejack smiled and nodded, flipping the pancake she was cooking.  
“Y’know your big sis loves you, right..?”  
There was a pause, before The mare felt a round, bony forehead press close against her side.  
“Ah know it. Ah know.”
 
…Setting a short stack of pancakes down on the table in her sister’s place, Applejack turned to fetch her own breakfast as Applebloom clambered up onto her stool. Like sleeping, eating breakfast was another activity the mare knew her sister no longer needed to do, but again, it was a habit. It was normal and it felt good. When Applebloom had first returned from Everfree she had been worried about her sister wasting food on her, but those worries were met with a mock-stern look and Applejack asking her who she’d be if she let her little sister miss a meal.
 
In the end they’d compromised. Applebloom sat down shakily on her stool and smiled, as best she could, knowing that after they’d sat at breakfast and Applejack had eaten they would go together and feed her own pancakes to the chickens.

“Applejack, maybe me comin’ inta town with you wasn’t such a great idea…”
 
“You hush now Applebloom. You got every right at be here, same as me. You juss’ hold yer head up an don’t let anypony tell ya diff’ernt.”

call it murder if you want, but would you rather feel yourself threatening to hurt the ones you love any second or make a quick end to ensure you don´t hurt them.

what she wants holds no matter once her will fades, and while it is sad the torture of feeling yourself become a monster is a fate we consider worse than dying, death means the end of life, but also the end of suffering.

What if that zombie is your little sister and doesn’t want to hurt anypony?

we studied protective instincts,but this one has a 80% chance of being suicidal. You don´t protect zombies, you end their misery.