I think lots of thick, cold custard and gravy (which she of course serves to the person sliming her) that could follow with baked beans, spaghetti hoops, mushy peas and maybe some cold jelly and trifles too for good measure?
I think in keeping with the outfits theme they should be lots of pourable substances like syrup, soups, treacle, gunge, custard etc. They should be in big beer glasses or jugs to represent the big beer glasses you get at oktoberfest, I also like Voith's idea too.