My 69 Year Old Mother Who Is Currently On Thyroid

My 69 year old mother who is currently on thyroid medication and medication for high cholesterol has symptoms of being very lethargic and felt a hot flash sensation while cooking over a hot stove. She has a family history of diabetes and her mother died of congestive heart failure in her 60's. She is concerned that it may be diabetes. I think it may be her thyroid. Please advise.