I am very to happy to say your mother is doing an excellent job on life style modification, as I can see you are concert about the fasting blood sugars probable her blood glucose levels are being rinsed in the night it could be more informative if can go through the medication or insulin she is on along with hba1c or she can be on agp (ambulatory glucose profile). And about the foods you are concern that has nothing to worry. She can have is actually much heather.
Please check your blood sugar levels from venous blood and through reputed labs because from finger tips you can only collect capillary blood which is not very accurate measurement. The portable devices are also very problematic indeed.