How does Aunt March's response to Marmee's note help to develop the theme?

Marmee's just received word from Washington that her husband is ill, so she wastes no time in packing her trunk and getting ready to head off on the long, arduous journey. Before she goes, she writes a note to Aunt March. In that note, Marmee requests some money from Aunt March; she hates to do this, but she has no other choice, as she needs to borrow some money for the long, sad journey.
Aunt March duly obliges, but in her accompanying note she says, quite vehemently, that she always knew that it was a bad idea for March to go into the army and that no good would ever come of it. She hopes that next time her advice will be heeded. Aunt March's response, though characteristically ornery and ill-tempered, shows that when push comes to shove, she'll do whatever it takes to help out. This is a prime illustration of one of the book's abiding themes: strong families will always stick together when the going gets tough.