Cera can't be a villain, as Sharptooth, and the Domeheads I guess too, fill that role.
However, she's not exactly heroine quality material in the first movie. She's stuck up, bigoted, and can be downright mean.
On the other hand, she's not exactly antagonist material either as, other than LBTs biggest Littlefoot vs. Cera fight, has never tried to harm him physically in that film (at least, not that I can recall.) Also, she doesn't seem to fully believe what her father says as she was with Littlefoot both before her father mentioned the "Threehorns don't play with Longnecks!" thing, and, knowing Topps, it's likely he's told Cera that BEFORE that incident, oh, say, a couple of times at least.
Also, even after that incident, it appears that she is still content to play with Littlefoot in the scene where Sharptooth comes along. So clearly she doesn't fully believe in segregation either. (Though, of the five, I think she believed in it the most and that can safely be said.)
I don't quite see her as a bully like Hyp, Nod, and Mutt, as she, though kind of a bully, seems sweet enough to not have that be her personality, is it is the case with Hyp, Nod, and Mutt.
Also, to her defense, even Littlefoot is caught parroting the segregation line at one point, telling Ducky that her type probably shouldn't play with Longnecks.
Also, in the book, Cera is even nastier, as she at first doesn't think Spike should go with them.
She seems like a rival to Littlefoot in this movie, and, I guess, in the book too, as the others either follow Littlefoot or her.
Also, despite running off in her pride, she does end up saving their butts from Sharptooth at a crucial moment (nor, interestingly enough, is this the only time she does this, as a very similar thing happened where she arrived in time to save Littlefoot in film IV.)
Also, the fact that she was too proud to admit she'd gone the wrong way (and hence almost led the others to their deaths) does, in a bit of a way, make her similar to Pterano, though he was worse as he was older and it took him YEARS to admit he'd been wrong whereas we can guess that Cera probably apologized soon after the end of the first film, and that, had Pterano apologized, he'd probably have been let into the Great Valley and never been banished.
Still, Pterano is the antihero of film VII and I think that this similarity with Cera, albeit on a much smaller scale, furthers my case for her, at least in film 1, being classified as an antiheroine.
So, do you think she is a misguided heroine or am I correct in labeling, at least for film 1, her as an antiheroine?