Since Eliza introduced herself as a Witch of Summer under the service of the White-Faced Bear, it follows that there might be a Witch of Winter as well. Bonus points that Eliza's power will wane as the comic delves into Oscar's winter and reintroduces Barbara as the Witch who protects the town during Winter.
First of all, Kevin is adopted, so we have no idea who his biological parents are. Second, when Oscar and Clifford discuss whether Nora knows about Clifford being a werewolf of not, Clifford is persuaded that she doesn't and mentions that there are many things she doesn't know because she's so busy working, without being specific. One of them could be something special about Kevin, for which Clifford is the Secret Keeper.
It was never specified what event during Cliff's birth put her off any further pregnancies. Perhaps Clifford came out in his wolf form? It certainly would make her naming decision appropriate.