When is a single chick old enough to join an existing flock?

Hi everyone,

I'm a newbie (sorry), so I'm not too sure if this question has already been answered on here somewhere. If not then here's the problem... I have four adult mixed breed birds that are established in their little coop. Recently, I acquired a silkie chick, and raised her indoors, she is about seven or eight weeks old now and has been outside for almost a week. I built her a little "mother in law" extension on the bigger coop. Now the dilemma; the other chickens will peck the chick like its going out of style when I range them together. They seem fine when they're side by side in their coops, but they all attack when ranging. Also I live in northern Washington, and it's going to get very cold at night soon. I'm told that chickeneers up here don't do anything special to keep the birds warm in winter, because they huddle together for warmth. But something tells me this little silkie wont be welcomed into the huddle. When can I stop mothering her and just throw her in there and let 'em peck it out?

Thanks for any help you can offer!
Drew