Honestly, right now she is much like an infant child or puppy - that nibbling and biting for all it hurts is just her putting things into her mouth to explore. She will absolutely grow out of it on her own, and probably quickly. Provide things she can chew on in her tub, and prevent her having access to your hands so you don't get hurt, but it will fix itself pretty well - though the company of other rats will likely also help both the biting and nervousness. *Don't* correct her per-se or you'll just scare or hurt the poor thing and do more harm than good.
And nervousness in general is sort of a stage in itself. Mice have something similar - and they turn into little popcorn fluffs because they're just everywhere as they become more aware of stuff around them and as prey animals that can lead to being... well aware that they're vulnerable. Again: Company and time will help.
Introducing again, I'd do. Doesn't have to be a drawn out thing, babies should get along well, but she's been getting used to you for a bit. Just do a neutral space and very clean cage n o one has been living in so it's all neutral territory and they'll be okay.
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