This. Why are people in any way surprised that Spock never mentioned her in TOS. He didn’t mention his parents until they were standing right in front of him, parents who BTW, did not attend his Pon Farr ceremony. He also never mentioned his brother. So the fact that he never mentioned his sister totally in keeping with his character.
What’s more shocking to me, honestly, is that Kirk apparently does not read the personnel files of his own senior staff. Cuz, you know, that information is probably in there.