Have a little time and was wondering. That lady in the op - figure she’s increased muscle and bone mass some very modest amount along the way but still, that is likely more than 1000 pounds of fat, call it an even 90% body fat. A shade over 100 lb of fat free mass (FFM) is likely it. Plugging it into that last calculator and assuming that at that mass her activity level is on par with a sedentary occupation (and a moderate protein diet), her food energy required to maintain is 2172. Up her FFM some, to maybe another 50 pounds of muscle, so she is down to 84% BF and give her credit for moving a bit more - to an occupation with prolonged standing - and she might increase to 3194.
In comparison an about 154 pound (70kg) person with 28% BF at the same intial less active level needs 2188 to maintain. At same last level of activity needs 2480.
This thread reminds me of an earlier one on a similar topic. I remember it because I took the time to list enough food to equal 30,000 calories (see post #10). It’s a daunting amount of food.
At 200 pounds and likely 45% BF she’d need 2467 to maintain and as noted 520 more to gain the weight at the rate to get there by 20 years. By 1100 pounds, if she increased her muscle mass a generous amount carrying that extra mass around, and kept up some modicum of normal movement, she’d need another 700ish daily calories to continue to increase at the same rate. That’s an additional 10 double stuffed Oreos above and beyond the extra Big Mac.
For someone with disordered eating not too out of range to do.
(Please note: that formula likely works moderately well on the way up but after weight loss metablism is not the same and fewer calories are needed at the same weight and percent BF by someone formerly obese - or more obese.)