hypoglycemic attacks ?

My Mum has been ill for just over two years but it is gradually getting worse. She is fine all day long until she eats. As soon as she eats, she feels sick, dizzy and weak. Most times she does end up vomitting. Her blood sugar levels do drop to usually around 4.5-4.8 which we have been told is not low enough to be a hypo even though she has all the symptoms. There is no pattern in these attacks. One day she can have one after every meal and other days she wont have one. she has fasted twice and no results have come up. Every doctor and specialist seems to contradict themselves. She has lost a lot of weight and now she is starting to avoid eating so she is not sick. I fear it is just going to get worse if not sorted.