Female rat becoming increasingly aggressive

Question
Hi Sandra

You had helped my roommate and me with an issue before and I trust your judgment. We need help with one of our rats getting more aggressive.

Our two girls are Ziva and Hermione both are about one year old. We got them from a woman who could no longer care for them. Several weeks ago Hermione got a respiratory infection. We took her to the vet and she gave her two weeks of Enroflaxin and Doxycyclin (not sure if spelling is correct). She also recommended that we separate them. Well, after the two week was up, we tried to reintroduce Hermione back into the cage and there was a major fight. That is when I wrote to you for your help. We followed your advice by releasing them into a neutral territory to play and feeding them some baby food on a single plate so they would have to share it. We fully scrubbed down the cage and after an hour or so of play we put them back. They sniffed around and then snuggled down in their igloo for a long nap. It was a success! (Thank you so much for your help, by the way!)

Anyway, they continued to get along with only minor squabbles here and there. I figured it was them just trying to re-establish the hierarchy.  But recently Hermione has become more aggressive not only with Ziva but with us as well. We can put our hands in the cage to play with Ziva but Hermione will try to bite us, unless we have food or a treat. Hermione does okay once outside the cage when we take them out to play, though one time she did bite my eyelid when my face got a little to close for her comfort. (Ziva is fine with this. She will sniff my face and let me give her kisses!) What I'm worried about is her hurting Ziva. One night, we we're awoken to a very loud squabble. It took about 10 minutes for them to calm down. We had to separate them by spraying them with a water bottle. They were really going for it. But we checked them out and they were okay.

However, a few days ago I noticed a small puncture wound on Ziva's front arm. Now it looks like a scratch. I don't know if it was Hermione that did that or if Ziva has been doing this to herself. (They do have lice and are being treated. They have another appointment for a follow up shot this week.)

Since we're taking them to the vet, are there anything illnesses we should have Hermione checked out for as far as the cause of her aggressiveness? Could she have been psychologically damaged from the two weeks we had them separated? What can we do to help her?  

Answer
It sounds territorial for the most part. How long have they been back together for?

Also so sorry for the delay. My email was bouncing back the mail coming in from allexperts so I just got this during a reminder !

When you take them out to play, where do they play and for how long?