It's crazy when you consider the math.    4 years = 4 x 365 = 1460 days. 420 additional pounds = 420 x 3500 = 1470000 extra calories.    This means that 1470000/1460 = 1006.85 extra calories daily. Which doesn't take much - that's an extra Venti starbeetus a day to gain 420lbs in 4 years.    But with each additional lb, her TDEE would increase slightly. So at her starting weight of 460lbs and assuming average female height of 5'5", her starting TDEE at the beginning of the 4 years would be approx 3400 cal/ day. So she started this journey eating 4400 cal  and only increased from that point.