Working from a set of assumptions about Queen Dead Last here, including her being of average height and 250 lbs (purely an eyeball approximation) I arrived at around 2800 calories a day to maintain her weight. The shortest class of ultra generally raced is a 50K. When I did my first 50K (it took me around 5 hours since I actually ran, albeit on all kinds of rocky terrain) I burned about 3200. I'd assume Tubbs burns more, on account of her weight and obvious low level of fitness. So I'd estimate that on race days she eats about 6500 calories, if she's not losing weight. For comparison, 6000 or so is the amount a person burns doing a full IRONMAN triathlon; the IM people I know have explained to me that they carefully develop a nutrition strategy, typically finding the most carb-dense and palatable foods (sodium is very important too) and eating every 15 minutes or so during the bike and run portions (of races taking 12+ hours). She evidently out-eats these people.