Risa

In the licensed fiction, there are a few versions of Saavik’s origin, but the most commonly cited one is that Spock found her as a hybrid Romulan/Vulcan child in an abandoned Romulan colony (sometimes named Hellguard). He then took her to be raised by Sarek and Amanda, visiting her regularly and eventually sponsoring her into Starfleet.

Also, in the novels, Saavik and Spock eventually marry, and that’s the wedding that’s spoken of. But how much you want to accept that depends on your squick factor. Given the longevity of Vulcans, the 34 year age gap may not matter that much (she was 65 and he was 99 when they were betrothed; 80 and 114 respectively when actually married).

(See https://memory-beta.fandom.com/wiki/Saavik)

She was once. Then she was played by Robin Curtis in her two later appearances. Which at the time was unusual in Star Trek.

Now loads of characters have had two or three different actors play them.