Two small problems
I saw two problems that are pretty small. The first is really tiny: it's that the theme song has only a limited connection to the story. It gives the impression that it's a romantic story, and it isn't.
The other one is a little bigger. The story implies that Mary was "inspired" to go to Spain and face the risk of death without even realizing that her brother was fighting against Franco. I suppose Mary could be that stupid, but it seems it would be more plausible if her brother had been fighting for Franco.
I don't know, maybe that's not a real problem. Perhaps the basic point of the film was to show how dangerous teachers can be if they have impressionable students. But the point would have been made just as well if Mary's brother had been fighting for Franco.
"Extremism in the pursuit of moderation is no vice."