Calories burned working on ER shift

Hello,

My girlfriend is a resident doctor who work on ER shift every 5 days.From 3 p.m to 7 a.m next day on weekdays and 24 hours straight on weekends. On those shift work days her calorie count usually surpases her goal, specially because those second dinners at midnight.
We guess that on all those work hours she burns some calories more than in regular work days or at home, but we do not have idea how to count them.
Anyone could help us?
Thanks in advance and sorry for my english.