First off, don't attempt to tame your breeders when they have babies. I have found that even my nicest ones can turn defensive when it comes to their offspring. Outside of the times when she has babies, just take her out often, pet her and spend time with her. Rats (unlike snakes) love the attention and can become wonderful pets with time. Some might never be friendly. I have a couple that are standoffish all the time and some that will hang out with you for hours, clicking their teeth constantly while being pet.