Jane's mom only shows up in one chapter, and boy, are we relieved about that. She complains about everything, from the city to the heat to Jane's apartment. She's a critical component of the story, though, because she really sets the whole plot in motion.
It's her idea for Jane to charm her dying Great-Aunt Carolyn in the hopes that Carolyn will write Jane into her will. "Call me the moment you learn the amount!" (2.1) she chirps happily, when Great-Aunt Carolyn finally kicks the bucket. Ah, we really feel the family love here.
If Jane is Elizabeth Bennet, then Shirley is an alternate version of Mrs. Bennet. In this version, she sells Lizzie to Lady Catherine in the hopes of profiting vicariously. Do you think any of Jane's mom's conniving nature rubbed off on her daughter?