I'm so so sorry for your loss. Yes, you did the right thing. Even though she had some capacity to enjoy life sitting in the window or snuggling, I think the loss of bladder control actually upsets them terribly. My dog (nearly 14) lost control over the last week of her lief, and it was so obvious that she just knew her time was up. I was ready to carry her outside, and set her down just to put on my shoes. Her bladder let go, and she was so upset - I could see it on her face. I took her outside anyway, but she just stood there looking at me. I even said out loud, "You're done with living, aren't you?" I know in my heart that she was ready to die.
I'm sure your kitty was even more fastidious than my dog (or most dogs in general). They groom themselves, they cover up things in the litter box. I'm sure her uncooperative body was distressing her a lot. You helped her to live for many years, and when the time came, you did the brave thing. You helped her to die. She needed you to make this decision because she could not do it alone. This was not hard for her - she was loved and comforted to the end. It's hard for you, I know. You weren't really ready. You never would be ready though, would you? But I'm sure your kitty was. She could feel it inside, feel her body failing. Animals deal with death better than humans most of the time.
What helps me is having a good messy cry whenever I need to. I just let myself feel the pain, but I keep it about sadness and I don't mix that up with guilt. I think the guilt makes you think there's some way she could still be alive. But that's for you - not for her. Does that make sense? The only way to minimize your pain would be to extend hers.
We made a garden stepping stone from a kit from the craft store. Neighbors of ours did the same thing. We each put it at the edge of the yard over our pets' grave or buried ashes. Another neighbor planted a tree. We made a contribution to an animal shelter. We read "The Rainbow Bridge" and cried our eyes out.
You heal, in time. There's no schedule for this so don't rush yourself or think there's anything wrong with you if you have days when you cry a lot, or a day when you forget to think of her for a while. It's all okay.