Cassandra's POINT OF VIEW (on JMT, and possibly her first album)), a collection of standards and originals, has a cuppla guest spots from Grachan Mocur III.
And then there's her work with Air, from way back in the day. Cassandra was once the Hot Ticket Du Jour in terms of being the "next great jazz singer", and back then, "they" really meant "jazz" in its unambiguous sense.
Point is, regardless of whether or not one loves or loathes her current appraoch, she's got a fairly deep history doing "straight" jazz, and doing it well. Some view her current direction as a sellout, others as a move into more personal territory. I fall into the latter camp, but that's not my point. My point is merely that whatever she does now, she does with a fairly significant jazz pedigreee behind her.