Poor girl! Best thing would be to keep them separate so they can't peck but close enough they can see each other and get used to their company for a little while: maybe a week or two. Providing lots of positive associations like treats or boredom busters will keep their attention off each other when you do finally integrate them again but also make them associate their presence with good things. Chickens can definitely be trained with food! Easy ones are hanging great balls with kitchen scraps, wrapping a head of cabbage or lettuce with twine and suspending it in the coop for pecking and snacking, hanging molasses and seed blocks, putting together fresh bundles of herb and hanging them upside down to dry and be discovered by the hens, chicken swings or extra perches for keeping away from each other, and just plenty of extra space and low stress :)