Thinking of next steps if we do suggest the wizard option, to make Heidi more comfortable with it, I think we should introduce her to Thorek.
He's very likely at the wedding, as he's a canny political operator and Kazrick is one of his apprentices.
As a canny political operator he should recognise the value of helping out the Empress and the heir to Reikland.
He's the second best Runelord alive, and if anyone else can manage what Kragg did and make another anti-Dhar talisman, it's him. With his experience with designing the Rooms of Calamity for the Colleges, he may even be able to make it more focused on helping a wizard survive their own magic, rather than including the spell-burning feature Kragg did, for example by including a miscast eating feature as well as a dhar burning one. Given the way his apprentices could selectively exclude all but one Wind from a material, he may even be able to do something like make a device that also produces a portable mono-Wind environment by pushing all but one Wind away, or consuming all but one Wind.
If he can do something like this, Mandred could live a much more normal life. His apprentices couod also make a mono-Wind wing of the palace for Mandred as they made Mathilde's mono-Wind tower, which may be much less suspicious to other nobles if we wanted to delay the reveal.
Given the Cult of Sigmar's relationship wi the dwarves and the saved examples of dwarven runecraft, a wizard-elector 'made safe' by such runecraft may be spun to be much more politically acceptable to the Cult, although that's perhaps a long shot.
As to why he would, as I say, he's a canny operator, and would see the value of Imperial favour,