It's probably too difficult for them to come up with a feminine version of "warlock" without using the obvious. I probably would have gone with something like "Presage" even though it sounds a little too X-men-ish or Haruspex, even though that sounds more like something you'd find in a Harry Potter book. But at least they didn't go with anything like Evocatrix, Harridan, Termagant, the Golden Magi, Doctor Enchantress or Captain Warlock.
Edit: And for the record,
I think I'll just call them "Herlock" for now.