Most people pretend to quarantine, as you stated, most backyard set ups are not set up to do so properly. If you don't do it properly, you may as well not do it at all.
If you have a high price flock, or a flock that you would go into a mental decline if you lost them, don't add birds. As don't add birds at all. It is a real risk.
If you only have a few birds, and you know and have been to the other place and seen her chickens and they look healthy, well it is not quite as much of a risk. Now, sometimes healthy birds can have been exposed to some and are still in the incubation stage, but generally speaking, healthy looks healthy. Technically if by chance you have visited her, and gone out to see her chickens and came back and went into your own flock in the same shoes and clothes, well you have already broken quarantine.
Personally, my maximum flock is about 12, sometimes more and sometimes less. I don't go to shows or auctions. People that are set up like me, I have often gotten birds from them, added them to my flock and done just fine.
What makes my blood run cold, is when people ( I belong to another forum and they do this all the time) go to auctions, shows and swaps and bring those birds home and add them to their flock. Those birds have been exposed to multiple birds and could have easily picked up something.
If you have enough space in your current set up, and the birds are the same size, I would just add them. Mine always seem to work it out with little bother. However, there is some risk. The above posters are right, you have to make the call.
Mrs K
