Tiredness, Sleepy, Fainted, On Birth Control. Can This Be Pregnancy Or Something Else Like Thyroid Issues?

I have a 19 year old niece, who recently passed out in the shower. she is a sophomore in college, however, she has been tired lately. she sleeps a lot and just does not have any energy. when she fainted in the shower, they could not find anything wrong at the emergency room. she was not pregnant and is on birth control . Her cycle recently came on two weeks ago and has not went off. she has an appointment with her Gyno doctor in the morning. Her mother took her to her Family doctor and they did blood work which results will be sent to her gyno doctor. her mother feels like all the test are coming back negative. What questions should she be asking the doctor. should she request an MRI , could it be thyroid . I assume at this point she may be anemic because her cycle has been on so long and she is a tiny young girl. But she has no energy, very larthargic and sleepy. the other day, she stated she felt like she was going to pass out she was so tired and weak. what could this be