Just the summae she actually reads, since glossing can be done simultaneously. That has already included Magic Invictus (Parma Magica) and In Flux Veritas (Muto) and will soon include Twilight’s Inevitable Triumph (Vim), Threading the Hermetic Needle (Finesse), The Grandest Jest (Perdo), and The Stag, The Hound, and The Prince of the Seven Crowns (Rego).
Of course that means that a non-Good Teacher wouldn't be able to gloss as many summae. But I admit it makes sense to combine Com + Good Teacher.
Okay, here's a simple proposal (simplistic?).
effective Com = (Quality + Level)/3 (round down) - 11 + simple die. Maximum 8, minimum -1.
The 11 was chosen arbitrarily so that Q+L 27 summae fit right into the (-1)-to-8 range.