Witchcraft - at least the kind practiced by Matira and the other members of her 'school' - is more masculine in nature than the minor miracles worked by the priestesses. The helmet Matira wears, for instance, is a representation of a god, not a goddess. Hence spectacles like this - as well as fireballs and summoning monsters - are pretty much her area.

I don't know whether this affected her decision to concede to Dion's request. But she knows her stuff...