I think there is a lot we miss by way of humor and ridicule from the writer about the time. Sometimes you read explanations of this and that about it (like Emma's not saying just plain Knightley even though Bingley is called Bingley with no Mr a generation earlier). We must miss a lot that Jane would be surprised about!

On the other hand, much of what we read and can't make sense of is just exactly how it sounds and is ridiculous! For Jane Fairfax's situation we have S&S to enlighten us. Remember the girls were raised very well and of a landed family and quite Gentleman's daughters. However their lack of dowries makes them looked down upon as wives. They still are at the same level as gentlemen of fortune and could catch one who doesn't care about their dowry (like Brandon).