The levothyroxine has a long half-life within the blood
and may also be withheld for 3 to 4 days without significant changes observed. The
Januvia and blood pressure meds you shouldn’t mess around with, so the experiment may not be performed completely. .
While you may think the diet has nothing to do with it, but I think investigating would be better than pure recall. You could try to make a log of things she eats and again try to make changes there depending on which foods seem suspect.