There is actually a reason for the emotions. Saavik was written as half-Romulan. They even filmed and cut a line that explained it.

The script for Star Trek II: The Wrath of Khan notes that, “Lt. Saavik is young and beautiful. She is half Vulcan and half Romulan. In appearance she is Vulcan with pointed ears, but her skin is fair and she has none of the expressionless facial immobility of a Vulcan.” (Star Trek Magazine issue 155, p. 62) Spock had a line where he stated this fact to Kirk in scene 5 after the Kobayashi Maru test, “She’s half Romulan, Jim. The admixture makes her more volatile than – me, for example.” Spock’s actually filmed line was however trimmed from the scene and not included in the theatrical version, the 1985 television version, or the 2002 Director’s Edition DVD release, nor on any of their home media formats. The line was included though, in a contemporary (prior to the “Wrath of Khan” moniker addition) promotional short, voiced by William Shatner. [2]

…

Kirstie Alley was somewhat uncertain if other fans would accept a Vulcan female and she endeavored not to make the unemotional female character seem too much like “a bitch,” by concentrating on the emotionality of Saavik’s Romulan heritage, which accounts for her crying on screen at one point. (The Making of the Trek Films, 3rd ed., p. 170)

…

It was Nick Meyer who removed the idea of Saavik being half-Romulan. He explained, “I didn’t see that it made any difference. There was nothing about her that was Romulan, so let her be Vulcan.” (Enterprise Incidents, issue #14, p. 62) Still, the notion of her mixed heritage has lingered on into the script of The Search for Spock where a script annotation for scene 229 stated that “[e]ven a half-Vulcan has a breaking point”, though it has remained unspoken in the movie.

https://memory-alpha.fandom.com/wiki/Saavik

So it wasn’t so much that Kirstie Alley didn’t understand Vulcans, it was that she wasn’t supposed to be fully Vulcan and it was Robin Curtis who decided to play her that way despite the script saying she was a half-Vulcan in the notes.