Just as the mage is going invisible, Harry informs Forty that the requested job is finished, and leaves the statement hanging with that odd mental pull that means the spirit would still perform another service.
Without really thinking about it she snaps back the request "If you would be ever so kind, great beast, to help take down the magician that had summoned the spirit you were fighting, I would be ever so grateful."
And to do her part Forty unloads a quick burst of stick-n-shock at the image of Kachina, cackling "I thought you'd never ask!"