...as something of value. JA earned I understand a few hundred pounds by writing and I suspect that had she lived longer and been able to build more of a following during her lifetime she might have earned considerably more.

Making a living as a governess would, as you say, have been a bad thing. The pay was low, and the loss in leisure great. With 500 pounds a year anyway, as you say, why bother? It's not like more money would mean an improvement in medical care - as medical care was pretty ineffective regardless of how rich you were. And what could an additional 50 pounds a year buy otherwise that would make up for the loss of leisure? Perhaps a carriage, but you'd have no time to drive in it. More sheet music - but when would you get to play it? Fancier clothes - but when would you get to wear them?

Writing would have been more of an option. I don't know how many women authors were supporting themselves by their pen in Regency England (I know JA did not support herself), but Aphra Ben made her living by writing in the 17th century, so I suspect it was a possibility.

Though making a living writing is tough work and requires I understand a fair chunk of both skill and luck. Quite possibly none of the Dashwoods expected that they had the skill to do so.