Additionally, my instructor is careful to follow canons, which leads me to believe that there is no canon forbidding the depiction of the Theotokos without Christ.
Do yourself a favour and buy this:
The ‘Painter’s Manual’ of Dionysius of Fourna. London: Sagittaurius Press, 1978.
Everything is explained there. All the do's and don'ts. It is a good English translation and cheap to buy. Most of the iconography we have of the Theotokos without Christ is inspired by the Akathist to the Theotokos.
Also buy this:
Ouspensky, Leonid. & Vladimir Lossky.
The Meaning of Icons. Rev. Ed. Crestwood, NY: St. Vladimir’s Seminary Press, 1982.
When I took a course on it my prof. said these 2 books are essential.