Do we actually know that Lizzy is an "avid reader?" We know she read some, but I don't know if she could be described as avid.

I have a hard time imagining Lizzy tutoring Jane in propriety, partly because I think that Jane's sense of propriety was a bit better developed. But that may be in part because her nature was in tune with the sense of propriety of the time.

I think that the factor that Jane and Lizzy do have in common is visits to the Gardiners. I'm not sure where it is, but I believe there is a mention somewhere that it was mainly Jane and Lizzy who visited the Gardiners in London. So books and her own observations may have had an influence, but I think that a big influence, if not the main influence, was the Gardiners.