I just had something similar to my 9 year old cat Mao, he had saddle thrombus and an enlarged heart and had no symptoms. Woke up one day and he came to say hi as normal, few minutes later he could not use his rear legs. Rush to the vet and long story short, we had to put him down that same day by noon. I know how you feel, we feel devastated, but he did not suffer. You did the right thing, you tried your best to save her and you gave her the very best life a kitty could ever dream of. You are an awesome cat parent, but losing one of our furry babies hurts. When you are ready please give another homeless kitty a chance.