"Can anyone help me understand this imbalance?"
She got the rest of her calories from body fat.
"How do you manage this imbalance for trips of 6-7 days?"
My approach is to gain 3-4# of body fat in the 3-4 weeks before a long trip and use it to make up the difference. It has worked for me up to 11 days so far, but at some point body fat will be used up and you will begin to cannibalize muscle tissue. In my case, I hypothesize that would happen at around 14 days based on my experience so far. There have been several fairly long threads on exactly this subject so far, mostly in "Food, Hydration, and Nutrition", but also, IIRC, in Philosophy and Technique. They would be well worth locating and reading. Also, RJ did a pretty good writeup on the subject on his Arctic1000 website prior to the Arctic1000 expedition. I am sure your query will get a lot of replies before long, so stay tuned. Lots of folks are wrestling with this problem and there are a lot of good ideas floating around in the community.
Your other option, BTW, is to carry more food, but that will limit the duration of your trips in short order if you try to carry 5600 calories of food/day.