Yes, it's too late to separate them for quarantine now, so it's a matter of watching and waiting. Your injured girl shouldn't be put back with them until she's fully healed. There are some great threads on BYC about integrating flocks, and I'll look for some links to edit in here. You can...
SpeckledHen, thanks. I did it a couple hours ago, and it wasn't fun, but it was quick and painless for them. I just apologized to them over and over and said nice things about them in a friendly voice so they would have a happy ending.
Quarantine any new animal, period. Such good advice.
I dodged a bullet recently by putting two young turkeys I purchased into quarantine although I didn't think they were sick. I'm going to cull them tomorrow. Yes, they cost money which is now wasted; yes, I'm already attached and feel...