I completely understand your suffering and that of your child. At this same age my son began having these symptoms, after numerous visits to many doctors and many test for years my son was given a test, though I apologize for not being able to remember the exact name, to measure the activity of his brain during wake time, sleep time and reaction to a strobe light and it was determined this was a form of seizure which he thankfully outgrew.It is a direction you may want to discuss with your doctor knowing the pain of a mother who sees her child suffering ,unable to get answers. Don't give up!
Does sound like hypoglycemic symptoms to me, which I've personally experienced from a young age. Reducing carbs (from sugar, grains) and focusing on protein, fat, only carbs from fruits and vegetables (more from vegetables, even fruits can be too much sugar) will help if hypoglycemia is the problem. You can find free info and people's testimonies at mark's daily apple.
I suggest you make an appointment with the doctor to check your daughter and run further tests.
As you mention the sugar levels, suggests that you are concerned whether she has diabetes. With her feeling dizzy and passing out may be due to hypoglycaemia when the sugar level drops too low.
The doctor will get a blood test to check her HBA1C blood sugar levels to determine if her condition is related to her blood sugars. This test gives an average reading over a 12 week period, and not the sugar levels on the time of drawing the blood.
Another reason for her condition could be low iron levels in her body and dehydration. Make sure that she has a healthy well balanced diet and plenty of drink, water, milk (if she is not lactose intolerant). Keep her off fizzy drinks and junk foods, processed and highly refined foods like cakes, white bread, sweets. Give her small meals and a healthy snack to eat in between. A blood test would confirm where she has anaemia or not. Sometimes a doctor can tell by looking at her skin and inside the eyelids.
Make sure that she has adequate sleep for her age. For example be in bed 8.30 to 9pm latest, with no reading or watching TV or computer games.
She may have a viral or bacterial infection and the doctor can examine her to find out if that is the case.
Best wishes.