Oh, god. I’m so sorry. And if it’s any consolation, I think I can definitely relate to your pain and grief.
Seven years ago, we brought a fresh bouquet of day lilies into our home from our garden. We did not have any idea how extremely toxic lilies are to cats. Our beloved cat chewed part of a petal. By the time we figured out he was sick, read with horror online about lily toxicity, and rushed him to the vet, it was too late.
The guilt was crushing. The grief was so strong and painful that I remember barely being able to sleep or eat for weeks. It’s still hard to think about.
What happened to your cat, though, was an accident. You love her, and all you can do is give it your best effort, keep her as comfortable as possible, be with her at the end if the end comes, and mourn her.
I’m close to tears writing this. I’m just so sorry for you. Seven years on, we have another rescue cat we adore, whom I adopted in the aftermath of losing the other one. I couldn’t stand the hole in my life in the wake of his passing. You may be different. But whatever you choose, please be gentle with yourself.