It's bound to happen sooner or later as you integrate different birds. We spray the victim with antiseptic/anti-peck, and leave her with the flock under supervision. With luck, it'll all settle down, and the smell of the spray will deter the other birds from having another go. If that doesn't work, then isolate her for a day or two to recover, then reintroduce her with the main culprit removed for, say, 24 hours.