This sounds like it might be a difficult question to answer. I recommend that she speaks with her doctor
. Some of these symptoms can be caused by any of the things that you have had checked already. The specific difficulty is that none of these symptoms are terribly specific, ie, they do not really pinpoint the cause of the problem to one specific area. Light headedness can come from a number of locations, but cardiac issues, nerve issues, and other vascular problems or concerns are some of the easy ideas that come to mind. Buzzing in the ear can also come from a variety of sources. Some people will have changes of ringing in their ears as they age, more of a constant phenomenon, and others will have these changes that seem to be affected to some degree by diet (such as increased salt intake). There are many other possible causes, and again, this is hard to pinpoint without more information. A hearing test may be quite valuable in this situation. Finally, feeling tired is one of the most vague symptoms that a person can have, with causes ranging from quite benign to quite severe. In light of the non-specific nature of her symptoms, she will need to continue working with her doctor, looking for clues. Consider a referral to a tertiary medical center.