Fluctuations in sugar levels. Chance. ?

My mother was diagnosed pre-diabetic in July. Hence, appointed a nutritionist to take care of her diet. Her Hba1c was 5.8 back in July, which went up to 6.0 in Nov and back to 5.6 in December. Today, she just had her fasting sugar levels checked which was 107, Above the normal range. This in spite of the fact that she is taking fibre rich vegetarian food and done away with all fatty stuffs which contain oil and non veg. She is not taking sugar except for morning coffee. She is taking more green tea and black tea without sugar. Moreover, she goes for walk every day and works most of the time at home. Having flax seeds before meal. She is not having any of the symptoms as well. Could the reports be wrong any chance..?