My Daughter Is Diabetic, Not Insulin Dependent, But Has Not

My daughter is diabetic, not insulin dependent, but has not been testing for over a year because she couldn't afford the strips. She is overweight but also very active. Her sister bought her a supply, because she was worried about her. She said her numbers were very high ?? but she's back on the diabetic diet for 4 days and her numbers have come down. Today she woke with a severe headache nothing is touching, even light bothers her. She's a teacher and made it through the day, but came home to go to bed now. I'm thinking it might be withdrawing from sugar, but don't want to miss something that could be dangerous. She rarely gets headaches. Thank you...never used this site before.