I have to kill my grandma's daughter

I'll start this with how we got here. My mother (45) had some recent lung issues and just got off steroids for it. She has asthma, smokes weed, and vapes. With that said she had an asthma attack which made her collapse in such a way my brother (19) could not roll her over to get her air until the roommate (40's M) helped move her and preformed CPR until the ambulance got there and continued CPR to the hospital, during which her heart stopped. They resuscitated her, but due to her brain not getting oxygen for an extended period of time, she has little brain activity and is experiencing seizures.

With all that being said, I (23 F) am the next of kin and have to make the decision to take her off of the ventilator and letting her pass or continuing her life for an unknown amount of time with no chance of recovery and letting her live in constant care. Knowing my mother, she would never want to live like that. She was a registered organ donor as well, and would be able to save 3 lives.

My grandma, my mom's mother, just happened to be visiting town when this entire thing went down. She's been by my side though everything, from getting angry at the doctor about bedside manner, to comforting me in a way I would have never been able to ask for. She knows her daughter would also never want to live her life hooked up to tubes and wires, bedridden and never able to live her own life again.

But I can't shake this guilt that I'm killing her only daughter. Her only child. The being she created and brought into this world, and I am supposed to take it away. It's eating me alive. I feel that somehow, deep down in her kind heart, she'll resent me. That she'll see me differently after this. That she'll have this anger towards me she won't understand but I will. I'll always know what I did to her. I took away her world.

What can I do to shake these feelings? No matter what I do I can't get over taking away her little girl.

EDIT- I've been talking to my grandma through this entire thing. She's been in on every conversation and is frankly glad i have to make the final say and not her, but she wouldnt put that on me in a million years. I wouldn't have been able to do any of this without her next to me. We've meet with the people in charge of organ donation, and we've started the progress. She will be taken of the ventilator and let to pass peacefully tomorrow or the next day depending on the timing of everything, I'm not sure how to describe the process rn.

I know I'm not killing her. I know she's already gone. It's just too hard to say goodbye to my mama.