nibbling on front foot/ weird moods

Question
I have two quick questions. First, lately my rat keeps chewing on her front toe a lot. I looked at it, and it looks totally normal. She's seems to be running and jumping just as much as she usually does.Nervous habit perhaps??? Second, my first rat has lived alone since we got her. We saved her from a snakes cage! We got a friend for her eventually and did the introduction process perfectly, but she kept brutally attacking the new one and I decided to leave her alone.so, I got a friend for the new one and they're are kept in my bedroom. Ever since, my resident rat gets in bad/weird moods every couple months. Easily spooked, stays in her cage and doesn't want to play. Then, after a few days she's normal again! Are a lot of rats this neurotic?  

Answer

Studies that I read during some of my research and time spent shadowing Vets at the clinic has led me to learn that rats that are kept solo can indeed be neurotic.  However, it sounds more like rattie PMS. Even though her estrus cycle is every 5 days, hormones can really play a big part in the way a female rat acts.  Sometimes they are aggressive and other times they are super cuddly.  

As for the rat chewing her toe....check it to see if there is a scab there or some kind of sore. Is her nail growing ok?