2 year old female with sudden odd behavior

Question
I have two female rats that are about 2 years and 2 months old, and one of them, Ziggy, has had a sudden onset of strange behavior. It started about 5 days ago. She started attacking the other female rat, by biting onto her skin (around her ears, neck, and face), and tugging on her until she squeaks. She does it non-stop, to the point where I have to isolate her because the other rat, Marley, can't sleep or eat around her. I have isolated her for hours at a time, but she continues to attack. She doesn't draw blood, but Marley is squeaking so it must hurt. She has done this in the past, when she was sick about a year ago, so I'm guessing that she might be sick in some way, but she's showing no physical symptoms. (By the way, when she was sick a year ago, I took her to the doctor and they gave her an x-ray. It showed that her liver was enlarged, so we put her on steroids for two months and she got better after that. I (not the doctor, who said she had a tumor) attributed it to her having eaten something like aspirin or another medicine that was left on the ground. but, she was also not eating or drinking, or moving very much.)
The only other strange behavior is that she has been taking the wood shavings I put in the bottom of their cage and taking them, one-by-one, to the top level of the cage, where their nesting box is. Neither of them have done this strange nesting behavior before. It could be that I just recently moved them to my new house, so they're in a completely new environment, but I've moved into four different places since I've got them, so they should be used to this by now. She doesn't have a change of appetite, change of sleeping patterns, or anything. She's acting like she's pregnant, but there's no way she could be! She seems awake, alert, and healthy, so I'm completely stumped! Do you have any ideas of what it could be?
Thank you so much for your help!

Answer
Sometimes a surge in hormones will cause changes in rat behavior. The fact you moved to a new place could also provoke her to act odd.  Rats are very aware of their new surroundings. This can bring on stress and cause them to act up. As for the bedding being carried up to the other levels: I have seen this with my own rats as well as other clinic rats and its just simply a strong urge to nest which can also be triggered by hormones.   Things should calm down shortly but if not, your vet could prescribe a low dose of liquid valium given twice a day to help calm her sown some.  Rats can take these types of medications with hardly any side effects. What would knock you and I for a loop doesnt even phase a small petite rat and thats due to their fast metabolic rate burning the meds faster than normal.  A good exotic vet should know this and not be fearful of using medications like this to treat small mammals.