Saavik

Did she change her hairstyle?

Saavik was a Starfleet officer and navigator on the USS Enterprise in Star Trek II: The Wrath of Khan. She was very "by the book." In Star Trek III: The Search for Spock, she was one of the officers on the USS Grissom who found Spock's "casket". When Spock was rapidly passing through many stages of live on the Genesis planet, she helped him through pon farr.

In the Star Trek expanded universe, she was half Vulcan and half Romulan.

Saavik was played by Kirstie Alley in Star Trek II, and by Robin Curtis in Star Trek III and Star Trek IV: The Voyage Home.