Biting issue with Female Rat

Question
I've read many web pages about this issue and I cannot seem to find an answer.  I am a new rat owner and made the mistake of buying 3 female rats from a pet store.  (I was not aware of adoption in my area or that people breed rats.) My two little ones are just great and have never even nipped me.  However, my larger rat is the problem.  When she is in a hiding place, she will bite and draw blood if a hand comes near.  When not hiding, she will nip at your finger tips, and sometimes bite, if she is in the first level of her cage (the cage has two main floors).  When she is on the second level, she does not bite or nip.  I think it is a territorial issue but, from what I've read, female rats generally aren't territorial. (And I'm sure she is a female, I've checked.) She does not bite, occasionally may nip, when outside of her cage during playtime.  I'm scared to reach inside her cage for any reason (fresh food, water, etc.) for fear of being bit!  I am not sure what to do to correct this problem as I do not know what the pet store may have done to scare her.  Thank you for the help!

Answer
Hi Tanya

The problem is, your rat doesnt trust you or feel safe because she knows you dont feel safe around her. I have trained many biting rats  before with one being my wild girl Holly.  
When you reach in for her she probably bites you right? She is trying to tell you to back off and leave her alone. This is why she bites only in the cage and not outside of it as much because she feels more secure in the cage. '
The fact you admitted that your scared to even reach in to grab her food dish tells me she is getting negative energy from you and in turn, that causes her to also not trust you and makes her insecure.

I wrote an article for my website about how to trust train scared and biting rats. Most rats bite for the same reasons unless aggression issues from genetics play a role, but that isnt the case here.

Please read over how to approach and handle a scared biting rat. First thing is to try to hide your fear no matter what. This will get the ball rolling.

Here is the URL:

http://www.freewebs.com/crittercity/trainingshyorbitingrats.htm