I’m getting a female bantam to add to my others, she’s about 10 weeks same as mine. How long do I need to keep her separated/Quarantined? My coop is in my garage, so would putting her in a large dog cage in my garage be ok?
Well if you are trying to quarantine - no it would not be ok, as it would be the same air space. To truly quarantine you need to have a great deal of space between them. 300 feet, I think, but check. Some people do quarantine, some people don't, it is a real risk. Do NOT take anything you feel sorry for.
Most people cannot quarantine in a small truly backyard set up. That is a risk you take.
If you are asking how to get them together, It would be helpful to add a bird from your current flock to her. There will be a dust up, and some aggression, but it is one on one. Adding a single bird to an established flock is a difficult integration.
A lot depends on the number of birds you have, and the space you have to work with.
A true quarantine should be very separate, not in the same space.and you should have a separate set of clothes and shoes, and do chores for your established flock before you do the new girl , and at least a month. Adding one chicken to a flock, can be done, usually, but not always. It depends a lot on the individuals involved. I did it, but it was only to two others, and the one I added was bigger than the other two.