Wizards can mainly only protect themselves from hostile spells, but there are some defensive spells that could protect a group from mind-affecting magic. Mortus doesn't know them, so she wouldn't be much help anyway.
I keep mixing up Collegium Theologica and the Wizard/Alchemists Guild.
Sorry! It probably doesn't help that I keep using different names for the Wizards' and Alchemists' School. I sometimes call it the Mages' Guild, or the School of Wizardry, or something like that. Possibly because the books also call it different things in different places.
The Collegium Theologica is the normal, non-magical university. The only time it has been relevant is when Anton the Cheaty Duel Guy went in there.
Cassilda went into a cellar in the Wizards' School. Janna Eberhauer is Deputy High Wizard at the school.