Why does my iguana become angry when I stick her in the closet?

For starters lizards need light. They receive some kind of nutrition from the sun, or UVB lights. Without lights it will lack nutrition. Plus adult iguanas may need a bit more space than a closet. Some people devote their entire backyard to their iguanas. Iguanas like places that have leaves and branches. I doubt that your closet has leaves or branches.If it is still young give it a tank instead.