Can't tell you how sorry I am to hear that, man. All the best to you both.
My first instinct, since it sounds like it's mostly noticeable after a workout, was some kind of blood sugar thing like you mentioned. Having a basic protein and carb shake during training would be the first step to work on that. It should also cut down on soreness in general, so double bonus.
If the bloodwork from all the docs came back fine, I wouldn't think it's anything major. Exercise usually has anti-depressant effects (endorphins and all that good stuff), so unless she's having the same symptoms seven days a week whether she trains or not, I'd lean towards thinking it's something training-related that can, hopefully, be corrected inside of a week or two. Obviously though, I'm not a doctor, I'm just a knucklehead who tells people how to workout.
Other than that, maybe re-examine her program and diet. If her calories are too low or if the training volume and/or intensity is too high, she could be due for a cheat day, an increase in total calories, a deload, or a change in overall routine.