Happens in music classes (performances) biology classes (field work) and others. I sort of hate the idea of it, but if it was in the syllabus and your wife knew about to it beforehand, then I'm wondering what recourse she will have. My students would probably just leave early if I did that in my classes. It really is annoying.

One of my BYU professors added a bunch of required music performances, that weren't originally listed in the syllabus, and I hated her for holding us to an agreement that she could change however she wanted but nobody else could change without their grade being affected.