Sometimes, in Author Austen's work you can see where some apple managed to fall far from the tree, but there is little here to explain Elinor's vast difference from her mother and nearest sister.
Do you suppose she takes after her father? Is the explanation only that she HAD to be practical, when there was no one else to do it?
That last is rather a pitiful conjecture. I hope it is not true. I would want everyone as nice as Elinor to have some thoughtless fun and irresponsibility as she grew up, not to be forced into staid, worried maturity by circumstances.