Hi, I'm so sorry to hear about Zoe. It sounds like you made the best choice in an extremely frustrating and heartbreaking situation. You very likely did give her a longer life, and one with much more love and patience, than she would have gotten elsewhere. Having an anxious pet is very difficult, and I empathize with you.
Please come back and write to us about Zoe as much as you want or need. Having to say goodbye to our dear friends is awful no matter the circumstance, and I imagine many of us feel a fair bit of guilt and regret, even when it was truly the only option left. It's so hard to work through, but it will get better. Wishing you peace and comfort this evening.
"How it is that animals understand things I do not know, but it is certain that they do understand. Perhaps there is a language which is not made of words and everything in the world understands it. Perhaps there is a soul hidden in everything and it can always speak, without even making a sound, to another soul." ― Frances Hodgson Burnett