Polish hens tend to get picked on more as they have those attractive feathers and skittish nature. The attack may have changed the flock's hierarchy and she may now be getting pushed around. Another couple of polish hens would help if that is the case as it can spread out the picking by the other chickens. Having a couple of the same breed together seems to help personality-wise as well and in many flocks the same breeds will tend to be buddies.
Or your hen could just be traumatized. Chickens have feelings, too, but therapists aren't exactly helpful to them (lol). Maybe she is fearful of the raccoon coming back when she looks around. Change around the pen a bit. Add some grass patches and a compost heap for them to play in. Also, check out my article on Homemade Chicken Toys. It can help the entire flock feel a bit better to have things to do or other distractions.