Fostering

My friend has asked me if I would take her remaining chicken - a little laced Wyandotte - a bantam I think.  She lost her other chickens sometime in the last 24 hours to a fox - cam home from work today to find piles of feathers.  The little Wyandotte escaped because she was in the nest box (broody).  I have six chickens - all different, and plan to introduce the new one late in the evening - I will open the coop and pop her onto a perch.  Should I then just leave them to it?  Is it best to let them re-sort the pecking order the following morning?  I am told the new girl (who I shall name 'little orphan Annie') is quite a feisty lady - if she is anything like my Wyandotte there could be a few fireworks.    Anyone had similar experiences?  Thanks