welcome to HCM,
as per the details u have given, it seems , dizziness
is not due to drinking a cup of coffee..it may be due to blood sugar isuues or change in blood pressure or vaso vagal attack...she needs to be examined properly and there after we can come to conclusion..
i suggest you to take blood sugar levels and also check her B.P and get a fresh ECG .. after that the consulting doctor will give you the cause for dizziness..
hope this will help u