[lqdc13]

You would expend more than 800 calories from breathing alone at the weight of 125lb.

The Base Metabolic Rate in the cited paper is still much higher than that even for people whose metabolism slowed down.

Normally, it's calculated as (9.99 x weight_in_kg) + (6.25 x height_in_cm) – (4.92 x age) – 161 for women.

So for her (assuming she is 5' tall and late 20's), to remain at normal weight and not move at all it would have been (9.99 x 56.699) + (6.25 x 152.4) – (4.92 x 27) – 161 = 1225

This is without any exercise. She must have missed some source of calories.