https://www.backyardchickens.com/articles/adding-to-your-flock.47756/A. You NEED to quarantine this new chick. SHe could be carrying all sorts of diseases. A 20 - 30 days quarantine is best.
B. Sticking her on the roost is a nope. Chickens recognize up to 80 faces - they know who they go to bed with and who they wake up in the morning with. If you woke up in bed next to a stranger, you'd have the same reaction you would if they strode into your house.
C. They will bully her, badly. If anthing, start with a setup where they can see but not touch her.