Why then would RC's be upset with the movie because it showed Mary going through birth pains? If I understand you, the RCC does not teach as dogma that Mary felt no pain. Is the RCC not correcting its congregants for some reason?
You are correct, the movie on that point does not contradict the dogmata of the Church. It does, however, go against the prevailing opinion, including highly esteemed doctors of the Church such as Aquinas.
At the same time, the movie has received positive review by the Vatican, and my priest recommended it. It does not mean everything in the movie is as Rome would have wished, simply that it is a good movie to watch and reflect upon.