Oooo, cool idea cunningrat.... Actually, check page 30 of Art & Academe: it says that (in the medieval paradigm) vermin spontaneously generates from an appropriate substrate (say rotting meat), and thus can be produced by Rego Animal magic applied to the substrate. So close to Rego Corpus....
PS: for slightly more information on Tranquillina's overall research plan, one can see this post or that post.
The specific question I'm asking for 1229 is: is it okay to invent ReCo spells that duplicate the effects of CrCo spells that she already knows?