just an idea....but is your daughter taking any medication...even multi vitamins??? my son used to vomit spontaneously while he was taking a prescription laxative(it didnt matter when the meds were given and it wasnt every day)(and my sons doctor also didnt care)but i am sure that was it because as soon as i stopped giving it,he stopped and has not vomited since...and that was three years ago...also, i "get sick" if i take a multi vitamin on an empty stomach.... .
if your childs doctor is not taking it seriously than please find another doctor...one that respects your gut that is telling you that something may be off....it may not be anything to worry about, but i wouldnt stop until i figured out why..... i wish you the best of luck and i sincerely hope everything is fine...R.