My Daughter Is 18 Yrs Old. She Weighs 88 Pounds

My daughter is 18 yrs old. She weighs 88 pounds and is 5' tall. She tends to have low blood pressure but she has always had that. It is a family trait. She is away at college and has been having fainting spells when she stands up, exhaustion to the point of falling asleep everywhere and anywhere to the point where she doesn't dare drive, and her heart races when she is sitting quietly. She has been to Emergicare and to the on campus health clinic. Blood panels come back perfect, glucose test is normal and are her hormones, thyroid and a more in depth iron test. Where do I send her for further testing? She has always been very active (gymnastics and diving). She did have mono 4 years ago.