From what I know of designing and playing tabletop RPGs (alot, dammit), I believe I can provide insight on this.
The D&D rules have a spell type known as dismissable, abbreviated as (D). Such spells can be canceled by the caster at any time, including presumably midcast. If he had cast this, and someone tried to redirect it, he could simply poof the flesh-eating critters.
However, this is probably not a redirect spell. It's a mimic spell, so rebound is likely the wrong word because we didn't see a bounce back. That means, it is her doll casting the effect posthumously. Her doll has poor control of it, which is why she almost was eaten anyway, but it was under its control rather than Q'Talda (and undismissable by her).