Fanny's mother is basically Lady Bertram's poor doppelganger, which is a fun German word for "double." Even Fanny notes the similarities between the two sisters and, had circumstances been different, Mrs. Price could have been as wealthy and luxuriously lazy as Lady Bertram:
Her disposition was naturally easy and indolent, like Lady Bertram's; and a situation of similar affluence and do-nothing-ness would have been much more suited to her capacity than the exertions and self-denials of the one which her imprudent marriage had placed her in. (39.5)
Mrs. Price's situation is tied to themes on the important determining power that circumstances have on characters and on the theme of possibilities. Mrs. Price appears to us as a giant missed opportunity. A different choice in marriage would have made her life much different. For one, Mrs. Price definitely made a bad choice in marriage, which is a running theme in this book. But in her particular subpar marriage circumstances, Mrs. Price is stuck with too little money and too many children. And also unlike Lady Bertram, who scarcely seems to notice her children half the time, Mrs. Price favors some of her kids at the expense of the others – namely her sons and her youngest, spoiled daughter. Whether that's a result of circumstances or natural inclination, it's clear that Mrs. Price isn't an exact mirror image of Lady Bertram in terms of personality.