I am by no means an expert, but sometimes we are so critical of what we've done in the past or left undone, and we blame ourselves when they get ill. She's 11, which means you have done pretty well so far. She has probably forgotten those first few years, so maybe you can forgive yourself for them too.
I only say this because when I lost my first cat to cancer, I was sure it was something I'd done. I don't know, maybe, but he had a good life, and I know I did the best for him that I could have, given the circumstances in my life. He never held a grudge, so I'd bet Sapphire isn't either.