I understand what you are going throug. I also have an 8 year old daughter who has a constant fear of throwing up, However, her's came from one particular day that she did get sick and vommited. She had never thrown up in her life, so that was the first time for her. Well, it seemed to have traumatized her to the point where she thinks she will get sick and do it again. Even when she has to burp, she thinks that means she is going to throw up and she runs to the bathroom and sits in front of the toilet. It is now starting to interfere with her daily school activities. She cries and cries a lot on and off before and at school. When they ask her what is wrong she says "i don't know". I truly believe that she now associates the school as a bad place because that is where it happened and she thinks it will happen again there. I have been called numerous times from the school nurse and couselor that she is crying again and that she does not know why. I have talked extensivley with her and asked if there is a problem at school and she is adament that there is noting wrong there, only that she feels sick when she goes to that particular class that it happened in. I have explained to her of that being the way the tummy gets bad things from your system and she understands but she just can't seem to let go of this fear and fearing that it will happen again at school. She is happy and normal at home, but she will somewhat make up illnesses and throw herself in a little panic of thinking she has to throw up. I too, am really concerned and searching for answers to remedy this.
First and most important, even though she is apparently not obviously ill, she should be checked medically because she may have a condition which actually results in a feeling of nausea. Part of the evaluation might be an assessment by a pediatric gastroenterologist. To be frank, in almost every instance of this behavior I have witnessed over a span of thirty years, ultimately a physiological cause has been identified. I am very reluctant to assume a psychological basis for such a reaction. Now, when children have gone through an episode, or a period, of actually vomiting, they sometimes carry the fear of doing so for some time before it wanes. If medical factors can convincingly be rules out, please do consult with a mental health clinician, and don't put too much emphasis on the embarrassment your daughter might feel.