I am so sorry to hear about your cat.
My co-workers cat developed a blood clot in his back leg and was in horrible pain. There was nothing to be done but have her precious baby PTS, diet change would not have changed the outcome. I do believe this may be caused by a heart defect.
Cat maid to:
Puddles, female Himalayan (16 yrs)
Jasper, male Ragdoll ?? (approx 9 yrs)
Sweet Pea, female silver tabby DSH (approx 7 yrs)
Rose semi feral, a cpietra rescue, female tabby (approx 6 yrs)
Snowball RIP (1991-2005)
In a cat's eye, all things belong to cats.-English Proverb
“While we are free to choose our actions, we are not free to choose the consequences of our actions.” Stephen R. Covey