That used to happen to my iguanas, and usually the culprit was rod-shaped bacteria in the gut. Easily treated with antibiotics. After she gets better you have to replenish her intestinal supplements that the antibiotics have killed off. These supplements contain the microorganisms that iguanas are symbiotic with so they can digest fiber into carbohydrates. Make sure to get a culture that is known to have living microbes. Find them at health food stores, and at high-end grocery stores.