I say a super-retro outfit. Instead of a utility belt, an apron with various pockets and loops for knives, etc.
And the serial killer idea is not bad- perhaps Dabberina is driven mad by an overabundance of processed foods, and goes on some kind of rampage...
Ooh! Ooh! Driven mad by the public's increasing reliance on eating out instead of cooking for themselves, Dabberina renounces the cooking life and withdraws into a life of solitude. That can be the Act I finale. And then during Act II Dabberina's henchman, Pressure Cooker, has to convince her that hger skills are too valuable to waste!
And these Keebler Elves- are they the main villain, or just a side gang? Who is the BIg Cheese of the culinary criminal underworld?