It was Javanka’s little party. That trip was not organized through State.
It would have been demeaning for State Department personnel to tag along at the last minute. So Rex was correct in passing on it.
Ivanka used to trip to spout liberal feminist claptrap. That's hardly the sort of event that requires US State Department participation.
Tillerson isn't exactly perfect (I think that he supported Jeb in the primaries, for one thing), but he's still a better representative of the US than Jared and Ivanka.