@Clara116
Wow, I have to applaud your efforts and everything you did to train Zoe, especially as someone who was not particularly fond of cats. She certainly is a beauty though, so I'm not surprised she melted your heart.
It's similar in a way to my cat Merlot, who was a stray who showed up in my back garden. All efforts to find his owner were in vain and the vet assured me that I was wasting my time as this cat was "born a stray, always been a stray".
There was no way you could touch him initially, in fact, you couldn't get closer than a few feet and, even once you could, there were plenty of hisses and a few swipes. I had to borrow a trap from the vet to get him there, which was traumatic.
After a lot of treatment (he was at the vets for 10 days because it turns out he had been hit by a car and would have died that day or the next), he came back home with me. The vet told me not to take him to the shelter because he would never get adopted and would live his life in a cage. I let him back outside but he kept coming back. I tried to fid someone to adopt him, but no one wanted this scraggy feral kitty.
So, I was stuck with him. Much like Zoe, it took baby steps to domesticate Merlot, but I was surprised how quickly he transformed. I think that it helped that I already had two very chilled, socialised and happy cats, so he took his cue from them and imitated them.
Before long, he moved into the house. Then, he let me stroke him and the hissing stopped. It took a lot longer than that before he let me pick him up and I did always wear some heavy duty gloves in the beginning. He still doesn't love being picked up, but there is no scratching, just some purrs, followed by wriggles when he's had enough. More recently, he's become obsessed with getting on my lap when I am working. I never ever thought this kitty would become a lap cat.
However, it's still a nightmare getting him to the vet's. I have tried all the tactics you used with Zoe, but it just doesn't work with Merlot. He has to be sedated and, even then, it takes two people to get him in. One has to wrap him up like a burrito and put him in the carrier, while the other is poised and ready to quickly shut the gate!
He is pretty well behaved at the vet's though. The first time I took him (after trapping him), he went insane and was literally bouncing off the walls, poor thing. Now, he's pretty chilled, but I guess that is probably because he's sedated.
Anyway, he's such a loving, affectionate cat. I never really wanted him in the first place, but he's very much part of the family now and I became very distressed when he went missing for a couple of weeks. Luckily, he did manage to find his way back home.