Why does Red Dress mistranslate the priest's speeches?

Red Dress is immensely grateful to the Jesuit priest for teaching her to read and write. At the same time, though, she cannot ignore the fact that he has absolutely no respect whatsoever for the Sioux and its traditions. To him, the Sioux are poor, benighted savages, pagans in desperate need of God's word. In converting them to Christianity, he will be contributing to the destruction of Sioux culture and the unique religious worldview on which it is based.
Red Dress goes along with the priest but only up to a point. She agrees to translate his sermons to the other members of the tribe. However, unbeknown to the priest, she deliberately mistranslates his words so that they make no sense. And as the Sioux can't understand the Christian message, then it is impossible to convert them. Red Dress's culture means everything to her, and by deliberately mistranslating the priest's sermons she is attempting to preserve the precious heritage of her tribe.