Ours will look like that if they get wet...are her back feathers still damp? They could be still damp and sticking together. And it doesn't look like pecking to me...Just messy feathers from the rain. Once they dry out more they should be fine. If they are damp, maybe you could try wiping her back with a dry towel or something to dry them and they should go back to normal.
i figured, but i wanted to ask...i know she is having trouble getting acclimated so it worried me. i had a baby in arms when i ran out earlier so just barely touched her...she was damp. i guess it surprised me b/c i have had chickens for a year and have not noticed this look on rainy days. maybe b/c she is white, maybe since she is getting picked on she's not able to shelter with the others. will take a towel out when my hubby gets home and takes the kids.
I agree. Our Splash Cochin rooster's feathers look like that when he gets wet and it takes a little while for them to completely dry...they will stick together and feel damp for a while, similar to yours.