"Her mind was less difficult to develop" — Jane Austen
Solution 1:
Once again, I find going to period-appropriate dictionaries helps make the meaning clear. In Noah Webster's 1828 dictionary, if we look up the word 'develop', we will see definition #1:
- To uncover; to unfold; to lay open; to disclose or make known something concealed or withheld from notice.
Her way of thinking is easier to understand than his is.
(This word is still used this way sometimes, e.g.: to develop film negatives.)
Solution 2:
To me, it seems like Jane Austen meant that her mind was less difficult to develop than her husband's, meaning that she is a lot less complex than him. Develop, in this context, probably means the entire process of her life and experiences to get her mind to where it is currently.
I don't think that the description was meant to describe her as stupid, but to descern that she's a lot simpler (and maybe a little more ignorant?) than her male counterpart.
Solution 3:
I think Austen means that Mrs. bennet is easy to read. She wants her daughters all married "well," and everything she does refers back to that goal. Mr. Bennet thinks a little more deeply, such as, will such and such a marriage lead to happiness? Does happiness require anything other than money? And so forth.