It is strongly implied in the movie that Pelagius was excommunicated for teaching that “all men are created equal” and advocating the abolishment of slavery and/or serfdom. In fact, he was condemned for teaching that there is no such thing as Original Sin, and thus, no need for the Sacraments, nor for sanctifying grace.
Is there any historical stuff I can tell her about?
Most of the movie makes absolutely no sense, from an historical or even a common sense point of view.
First, the family they are supposed to rescue is on the north side of Hadrian’s Wall - yet, somehow, they have walls and patios made of marble (marble comes from Italy; they would have needed roads and carts to transport it; neither of which existed on that side of the Wall, in that time period).
The Villa is full of valuable stuff - gold, gems, etc. - yet, for some reason, the Celts have never come raiding, despite the fact that the guards are native men who’ve been enslaved, who are obviously not treated very respectfully by their master. :shrug:
The battle scene three days later also makes absolutely no sense, since although when they arrive at the Villa, it seems to be the middle of summer, somehow, three days later when the battle takes place, it is the dead of winter and they are fighting in a blizzard, on ice that is thick enough to walk on. (If you live in a southern climate and your sole experience of ice is in your freezer, you might not be aware that it takes several weeks of sub-freezing temperatures for a large body of water, like that lake, for example, to freeze solid enough to walk on.) :shrug: