I'm really happy to hear this as this is also what we've done with our sick hens, and I always felt guilty because of reading everywhere that quarantine was really important.
We have bought a big dog cage for that use. Whenever a hen is feeling unwell we put it in the coop and we put her inside. We've found that if they are feeling really low they will let themselves be caged, if they struggle we let them out and leave them be and either they get better, either it gets worse and then they will accept being locked in the cage at that point.
We did have to isolate a hen that was really ill in September for nearly three weeks. When she started getting better we tried to put her in a pen next to our flock's place and she was just standing there watching her friends and being really depressed. As soon as we put her with the other girls she got better, even though she was slower and tired at times. We gave her some rest times in the first days and helped her to roost, and gradually she went back to normal. I'm convinced being in isolation was a real stress for her and part of her recovery was due to being back with the flock.
Dotty looks so funny! Guess everyone has a Dotty among their chickens

.