Ok so your saying exactly what I said, she's used to show Kong's more then a giant monster. Still doesn't make her the main character. You could argue that she is for the first hour, but once Kong hits its his movie from that point on (And seeing as the movie is three hours, two hours is definitely enough time for Kong's story). Without Kong the whole movie would fall apart.
Actually, it does make her a main character.
Here's how you can tell.
When you can remove a character and it impacts the plot and emotional impact of the film?
That's a main character.
And yeah, Kong is a main character too.
By your own admission, she is a main character for the first hour at which point is sounds like you're demoting her from being a main character and promoting Kong to main character status. Continuing with that idea, Kong isn't a main character until hour 2+.
BOTH are main characters from that point on.
The ice pond scene? Impossible if she's no longer a main character. Likewise with removing Kong.
What I think you're TRYING to say is that they're focal characters.
http://en.wikipedia.org/wiki/Focal_character
In any narrative, the focal character is the character on whom the audience is meant to place the majority of their interest and attention. He or she is almost always also the protagonist of the story; however, in cases where the "focal character" and "protagonist" are separate, the focal character's emotions and ambitions are not meant to be empathized with by the audience to as high an extent as the protagonist (this is the main difference between the two character terms). The focal character is mostly created to simply be the "excitement" of the story, though not necessarily the main character about whom the audience is emotionally concerned. The focal character is, more than anyone else, "the person on whom the spotlight focuses; the center of attention; the man whose reactions dominate the screen."
The focal character is also not necessarily the same thing as the viewpoint character, through whose perspective the story is seen. In Sir Arthur Conan Doyle's works of Sherlock Holmes, Watson is the viewpoint character, but the story revolves around Holmes, making him the focal character.
MORE:
http://en.wikipedia.org/wiki/Viewpoint_character
Sam, Optimus and Bumblebee are the focal characters.
Optimus and Sam are the main viewpoint characters. Their viewpoints coinciding over the course of the film brings both storylines together. In essence, making the audience that sympathized with Sam, carry that over to the Autobots, specifically Optimus and Bumblebee to a lesser degree due to his limited narrative qualities.
All the other characters are secondary to a large degree.