To me the characterization of Carolyn in the film is very much like the early Carolyn of the '66 eps. Both are very much bored with and resentful of life at Collinwood and want to seek excitement elsewhere. The difference, though, is the '66 Carolyn, being two years older, has ways/opportunities to pursue that excitement, whereas the Carolyn of the film is too young to go out to places like the Blue Whale (and to pursue situations that were too old for her). I honestly suspect that if the original show were to have begun with a 15-year-old rather than a 17-year-old Carolyn, she may have been very similar to the frustrated Carolyn of the film.
Also, the rivalry between Carolyn and David, even though it was all too briefly touched upon in the film during the first dining room scene, is in keeping with their relationship in the early eps. Early David liked nothing better than to embarrass Carolyn and get her into trouble, which the film's David certainly does in that dining room scene - and at times '66 Carolyn would have liked nothing better than to have smacked David into the middle of the next week, something it's easy to imagine the film's Carolyn would have dearly loved to have done, especially considering she called him "a little shit."
Plus, the '66 Carolyn often locked horns with Elizabeth - though that aspect of the film's Carolyn and Elizabeth is more spoken about than actually depicted in the film.