A few alternative interpretations:
Uhura tries to negotiate with the Klingons and lasts about thirty seconds before they try to kill her, necessitating that she be rescued. She later distracts Khan just enough for Spock to take him down.
She contributes, sure, but she's hardly a heroine.
You seem to have missed the part when she stole the Klingon's knife and stabbed him in the balls with it just as Khan started shooting. . . .
That was awesome. Heroic, even.
UHURA STABBED A KLINGON IN THE BALLS!!!
If that's not good enough for people, well pfft.