Bratty chin?

Hi, I'm Sarah. I've had 2 chinchillas from a previous owner since June of last year. The older one, Belle, is around 4 or 5. She's getting very comfortable with me and will sit on me and sleep, accept scratches most of the time (occasionally she'll squirm away), and doesn't mind being held-- AFTER I manage to pick her up. (She hates that part!)
The other one, Auroroa, is 2ish. She's kind of a brat and I'm just wondering what the best way to handle her is? I don't pick either of them up much, because when I try they run away scared. Auroroa is practically impossible to catch. She also tends to bite (pretty gently, but definitely not just a nibble) if I try to pet her, or sometimes she'll run up to my hand and bite my fingers for no reason. I always tap her lightly on the nose and say no after she bites, which I've read you're supposed to do, but this seems to make her even more scared of me. She still runs whenever I move around and doesn't let me pet her and squirms if I manage to somehow catch her to pick her up. How do I get her to stop being terrified of me?
(She will hop over me and sit on my lap so long as I sit mostly still and don't try to touch her. )