sharon, it's okay. You did what you could do at the time. We do what we can with what we have. It's okay, you did your best.
I am currently feeding my cat through a tube. The doctors told me if I didn't, she would die. Now after 3.5 weeks of this, and lots of $$$, I am not sure if this was the best choice. There are days she looks so sad, and I often wonder if I should have just put her to sleep then... that maybe it is just her time, and who I am to interfere. It's so hard to make these kinds of decisions, whether we should go through with treatment or not. We are not God, and we do the best we can with what we have.
Please just forgive yourself. Your kitty was sick. You took her to the vet. You did what you could, and I'm sure kitty was grateful.
You were a good Mommy... your kitty got sick, and you weren't the blame for that.