Iguanas who were already healthy can go literally for weeks without eating (but they do need to drink often).
Stress reduces appetite, so she may just be in some physical or emotional pain, which may go away in several more days.
Iguanas do not always breathe evenly and steadily - they often breathe in, hold it, then breathe out. Especially if they know you are watching.
I expect more from reptile vets. Can you find a really good exotic animal vet? There is an easy, not-very-invasive way to test for stomach perforations.