Another thing senators do is cast votes to spend other people's money. Caroline Kennedy should be very good at that. She grew up in a wealthy family. Her stepfather was one of the richest men in the world. Now she's married to a wealthy businessman. She's had lots of practice spending other people's money. She'd be good at it.
All this is not to say the job of a senator is easy. Senators do have to figure out which interest groups to reward with subsidies, special tax breaks and pork in order to assure reelection. But with a little work, that's probably not hard to learn.
So by the standard of the actual duties of a U.S. senator, Caroline Kennedy is eminently qualified.
But, of course, so is virtually everyone else.