This would be a tough one as she probaby has a rason to bite, 2 years of dealing with lab. people, I'd bite too!!

First make sure you do not smell like any food, and be very patient. Just lay your hand in the cage, eventually & slowly start to move your hand, pet her, offer food treats etc...

This may take some time & I do not meen to put a damper on you but she is getting up there in age, especially for a lab rat. The *average* age for rats is about 2 years. But look on the good side she gets to spend the last of her life in a loving home!!!! HOORAY!!!
maybe others will have more info for you! Good luck!