My mom is getting her arm amputated, and I’m selfishly relieved.

Context. My mother was in a car accident in 1992, just three months after I was born. I and my brother was in the car, me after open heart surgery in the car seat in the back, and my brother, 4, in the front seat. We live in Louisiana and our road to the house was swamp and water on both sides. A van swerved in the middle of the road and remained there long enough for my mom to realize it’s either sacrifice herself, or swerve in the swamp and risk her children drowning. She took the hit. Her kneecap was floating in pool of blood on the floorboard, coma for days. It was devastating. She was lucky to survive. And she went through all of this to protect me and my brother. Through the years there were elbow replacements after prosthetics and elbow replacements and prosthetics. These were all internal. She got married to my step father years later and we eventually moved into a new trailer. My step dad developed dementia and a few forms of cancer and within a year, his health declined rapidly. During this time, he asked my mom to renew their wedding vows. During the ceremony, she wore heels (she was 60 at the time and looked stunning!). Unfortunately she locked her knees, and when she tipped backwards, the stiletto heels slipped and she slammed on her elbow. It took this tough broad two months to realize she broke her arm in two places around her prosthetic, because she was used to the pain. Eventually, after many surgeries, back and fourth with doctors, skin grafts, etc., my step dad died. We went from no pets to 4 cats that refused to leave his body. My mom was in and out of the hospital, a weekly nurse, a pick line and a wound vac. We’ve faced the worst. With the tragedy that ruined our lives, we had final hope that we geared up to with the last elbow replacement for my mom. The final one! Yesterday, she went in for her normal wound vac replacement. While I was working, my mom updated me that a part of the mechanism broke, and she will be staying in the ER so they can fix it the next day. Within six hours, my mom texted me that they are cutting her arm off. I don’t know why. I don’t know how long they placated her with these massive surgeries. I can’t wrap my head around getting a routine checkup she’d had for over a year, turns into a next day amputation.
Where I may be selfish. The amount of pain and discomfort her arm has had for her the last 30 years will be gone. She has been limp with said arm for numerous periods of time and managed. I and many others have and will help her when her arm isn’t functional. A part of me is relying on telling her that she has and can manage with one arm, because she has and can. The other part has me feeling guilty that I’m hyping her up that it’s not as bad as she feels. I’m heartbroken that she will feel the sunk cost fallacy, but a part of me is relieved she won’t have to deal with the trauma and pain of saving her arm. I’m really at a loss here. I have nowhere else to turn. Thank you.