I would second the "hi-strength" approach. Either a hi-pressure steam cleaning or hi strength chemicals. I haven't heard of a way to do this without making a mess, but you can limit the mess with cardboard, plastic etc as stated earlier. Oven cleaner works pretty good, but usually takes a few rounds. Typically it's a nasty and time consuming task. I brake it down into sections and tackle it over several days time. The better you degrease, the less you have to deal with later on! Good luck with her and keep us posted.
Dan
