Oh dear you do have a quandary. Millie sounds a bit like my Sam, he has aggression issues that led me to adopt him from his previous owners, as he had started to attack, turned out to be a food allergy (intolerance actually) to grain and cereal.
If I gave Sam what Millie is eating, he would attack everything in view, so may I suggest a change of diet for Millie to grain free food before she destroys everyone's confidence? You may be surprised. Chuck the Whiskas and try Applaws or James Wellbeloved dry foods, see if there's a change in the next couple of weeks (it usually takes Sammy a few days for the carbs to leave his system) but once it has he's my loving puddy again.