Hello and welcome to the forum
Pet shop rats don't tend to be very well socialised, so your girls need to gradually learn that people are nice! This might take some patience but they should come round eventually. Do you know how old they are approximately?
When you say she is biting, could you describe what happens when you put your hand near her? Rats tend to explore things with their mouths and may sometimes grab a finger and give it a little nibble just to check whether you are food or not; if they are being a bit too enthusiastic a high pitched 'eeping' noise can let them know that they need more manners. But obviously there is a difference between 'test' biting and proper biting...I'm not really an expert on this so will leave advice to someone who knows more than I do.
It's possible that the biting is through fear, in which case she will take time to get used to her new environment. Try taking all hidey holes/igloos out of the cage and only give them open beds for a while; this will help them realise that even out in the open nothing terrible is going to happen to them. You could also try offering something nice (like yogurt) on a metal spoon - both rats will have to come close to you to get to it, and if there is any biting it'll be metal that they bite, which should help deter them.
Hopefully someone else will come along soon, but I hope this helps in the meantime
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