2 year old health declining/ i failed her

My Tux cat was just diagnosed with stage 4 kidney failure, i feel like i failed her, im emotionally destoyed right now, i adopted her 2 years ago during a freeze, when she showe up at my door step. Doctor gave antibotics and some lactose to help her go to the restroom, she has all the symptoms. Limp, hiding, not eating, drank some water. I live alone dont have anybody or human interaction throughout the week due to my job, this is all i have. I dont know if i should euthanize her yet or give her all these meds, i just dont know. Im in tears typing this. It sucks going through this alone. Angie is my everything and i failed her idk. Wish everyone the best of luck with whatever they are going through. Thank you for listening.