Oh, nowa, as a pet owner of many many decades, I understand your pain and your guilt. Honestly, I don't think it is possible to share our lives with animals without going through this.
It doesn't sound like you neglected her medical problems, and you
were trying to treat her - the fact that you took her to a different vet may be an indication that your first vet was complicit in pushing continued treatment and that you felt guilty for refusing it - is that a possibility? I certainly felt that way a year ago when my hyperthyroid cat was failing as the underlying kidney disease finally started to progress - as it always does. I refused hospitalization and further treatment because of his age, and I acknowledged the resentment I felt against the vet I saw (not my regular one) for being judgemental and pushy. And I chose another clinic for the euthanasia. I recently adopted a foster hospice cat who might not have long to live (some kind of liver thing going on) and when my new vet mentioned possible surgery, I told her I am not going to subject him to invasive measures, since right now (7 months after his shelter arrival as an emaciated stray) he is doing really well and enjoying life at age 13.
Do I have doubts about either of these decisions? Or about similar situations in the past? Of course I do - because our brains are designed to doubt! But I'm going to hold firm once again, and not succumb to guilt. This is a conscious choice.
You don't have to forgive every decision you made - sometimes we have to say "that was not the right thing to do" (for instance, not going in to be with your cat at the end) but you can also say that you were doing the responsible thing, and that she was in kind and competent hands - and then make the choice to move on. When you think of the many animals who do not receive the kindness of a peaceful end, you must be able to acknowledge that you did the very best that you could at that time.
And ultimately, you can certainly forgive yourself for the dark place you were in at the time. Also, please acknowledge that fact that by having enough love and compassion for yourself to be here, doing this work, you are making a significant change that will allow you to move on with your life, with clarity and better purpose.
And I just saw that Andy has responded - what he says, too
Peace to you,
Jan