However, in describing what we can infer was an encounter with a particularly desirable female, he said "Yeah, she was nova, that one."
I'm pretty sure it was "She was a nova, that one," and the Blish adaptation agrees. (It was in Star Trek 8, by which time the adaptations were pretty verbatim.) It makes more sense that it would be used as a noun than an adjective.
It does sound a little anachronistic to me, though, since the usage of "nova" has shifted over time. It used to be used synonymously with "supernova," and fiction continued that practice far longer than scientists did, but these days I hear "supernova" a lot more often than "nova" (even though classical novae occur far more frequently than supernovae). For that matter, if "supernova" had come to be slang for an especially hot person of one's preferred gender, that would make "she was a nova" rather faint praise in comparison.