traciebosket, currently, nothing that's native to Canvas would allow your instructor to run such a report, but you're going to love the solution that @James has developed in How to Count Student Discussion Posts. It's easy to set up and only requires basic Google Sheets skills.
As far as a built-in solution, the feature idea has been floated before the Community on at least three occasions (and James provides the links to the archived ideas at the top of his blog post), but thus far it has never received a high enough vote total to be moved forward for additional consideration. So I hope James's solution will do the trick for your instructor. Keep in mind that you don't have to be an admin to run this report, as anyone can generate an access token for the purposes of this report; the access token will have attached to it only those permissions that are attached to the user who has generated the access token.
