Did I killed her?

Yesterday I had to put her to sleep, but now I regret it so much, I think that I killed her, that I should have let her go on her own time. What do I do? I feel awful, I never wanted to do that, I don’t see myself ending something or someone, that’s not me, I feel awful.

She was a 14-year-old Persian, her kidneys were failing, they said she had lost 60% of it, her sugar was low, her red blood cell count was very low, she was extremely dehydrated, she lost almost all her muscle mass, she had a lot of issues in her uterus.

She was with my parents before they let me take her to my house last month and when I went to the veterinary and they told me all of that I got so angry about how could they be so negligent with her.

They bought her with the idea to make her have babies and sell them, it started wrong already, then later they ended up never doing it, and they never nurtured her, and they simply forgot her, it was like she was furniture in the house or a stuffed animal.

On top of that, they told me that I was wrong, that it's normal for cats to vomit every day and have diarrhea regularly, they never took her to the vet, they always had the excuse it was normal, and when I told them the truth about all the bad things they did to her they blamed it was her age, yes okay, but if you would have taken better care of her she wouldn't have spent her life vomiting every day and wouldn't have spent her last 3 years in pain when someone would touch her, and maybe she would have lived more years, and without pain as well, anyhow I get so mad with this kind of people.

Edit: thank you to everybody who commented, I'm still very sad but time will heal me, I didn't kill her but I was the one who God put in her life to finally give her peace.