Sudden Behavior Change

Question
Hello, I'm not sure how to start this so if it sounds rambled I apologize. Here goes nothing.

I've had rats for quite awhile now. I currently own 11 (5 boys and 6 girls) Mostly because I brought home my frist girl and she ended up coming home pregnant because of miss-gendering at the petstore. So I kept her offspring because I fell in love with them all. I hand tammed them, play with them daily, keep them well fed and well watered, with plenty of toys and running space in their cage (which is HUGE). The one in particular I wanted to ask about, she's almost a year old now. I've never had any problems with ANY of my rats. But last night, she bit me, and drew blood. It shocked me so bad because she had always been the sweet one. But now any time I go near her she squeaks loudly, acts like she's digging at the cage bars to get to me, and bears her teeth. I'm slightly worried about this. What could be wrong?

Answer
 It's possible that something stressed her and she is acting out.  If this is the case she should calm down eventually.  If she is near the cage with the males she may be stressed smelling them, fearing that they will hurt her.  It also may be a genetic thing; some rats that are raised properly and well socialized will turn out to be aggressive or fearful just because of their genetic predisposition to.  I had a fearful female who I rescued that was pregnant and though I handled all of her babies the same amount one of them turned out just like her mother, terrified and squeaky when handled even though she was fine when she was a baby.  I ended up breeding one of the males who was perfectly fine before I realized this and one of the girls in his litter turned out a bit off as well so I know for sure that there can be some kind of genetic bad behaviour going on.  Another thing to suggest would be to make sure she isn't pregnant; some rats turn more aggressive when they are pregnant, if she got anywhere near the males for more than a few seconds it is a possibility.  Also, make sure you wash your hands before handling her so she doesn't smell any strange scents.

 When a rat becomes aggressive for apparently no reason it can be extremely hard to fix.  Fearful rats can usually be tamed down, but if she is coming at you aggressively it means she is not afraid of you but it still being aggressive.  I do hope she gets better, but in my experience they often don't if there is no real cause for the change.  I really hope everything turns out, good luck!