"well none of her new in-laws have what you would actually call a proper job do they?!"
The Countess of Wessex tried; but faced non-stop criticism (potential abuse of connexions, and actual set-up). The Earl attempted various enterprises, but proved not to have the necessary acumen; but he did give it a go.
HRH Prince Andrew really flew helicopters during the Falklands War (and Prince Phillip's rack of medals were nearly all really won on military operations in WW22
HMQ is reportedly still able to strip the engine out of a 4-tonner (her wartime service as a mechanic).
The Princess Royal won Olympic Gold. Zara Phillips might do the same.
I can't see what Kate could havce done - other than go back to university. Even charity work would have led to accusations that she was presuming on a status she had not yet got. She'd have been papped out of any normal job, and a major target for press set ups.
I think they got it right in seeking a relatively protected position for her. Unless there is a poster here who works for Party Pieces, we simply do not know what her working life has been like. Even if it was fairly mundane, that's hardly unique for a graduate these days, is it?