AITA for euthanizing my girlfriend's cat?

Hey Reddit. I (41M) just lost my girlfriend (36F) of several months, who we'll call Noelle. Noelle has many cats whom she loves. This particular cat was named Sprinkles, who was definitely on her last legs. She cherished the cat by dressing her up, taking her out for Halloween, etc.. Fast forward to a few days ago. Noelle told me to give the cat her medicine because she was going to the hospital for my inferior who got ran over by my boss's car, but that's beside the point. She wrote Sprinkles's feeding instructions down for me, but it was too much to process. I had to give her a diabetes shot, roll the insulin in my hands, don't shake it, give her an ace inhibitor with her meal, to put her in front of her meal or she wont' see it because she had a cataract, mix one capsule of omega fatty acid with her kidney medicine, 15 minutes after she eats, and to apply a fungal cream under at the base of her tail. As you can probably understand, these are a lot of instructions, and I decided to do what was best for the cat: put it out of its misery. I euthanized it and put its body in the freezer. However, I did sing Sprinkles her favourite songs so she would feel at ease, and it was beautiful, and gentle, and respectful.

As a beet farmer, I stand by this decision, and did what city folk would not do. Sprinkles had no quality of life and she had no utility, as cats do not produce meat, or dairy, or anything useful.

I tried telling Noelle I'd be willing to taxidermy the cat, and to bury her at the east field by mother, but she pushed me and went away. Now, Reddit, answer me this - am I the asshole for what I did to Noelle's cat Sprinkles?