She shakes her head as if to say, "What the hell have they gotten themselves into now?" Whether she knew that Spock had died isn't clear, but she clearly has the look of someone who knows the people on board the ship.
I wholeheartedly agree. The people in the cafeteria / lounge seem surprised to see the Enterprise
battle-damaged like that, therefore I assume this is rather Excelsior
personnel enjoying free time than a "welcome home" committee.
For what it's worth the original pre-production sketch of this scene featured the Excelsior
alongside instead of the Enterprise
And in ST VI we see here serve on the Excelsior
under Captain Sulu. Maybe in ST III it was not her shift on the bridge, that's why we didn't see her there already.
And it's a good thing to think she was already aboard the Excelsior
under Captain Styles. At least it wouldn't look like she was asking her old "friend" Sulu for a favor, but got there on her own ("The Man Trap", were the two lovers?).
Had I not seen publicity stills of her with the Vulcan salute from ST IV I probably would not have noticed her. I don't really think she was supposed to actually play Janice Rand, but it was a nice insider thing for the fans to notice.