A lady should absolutely cover up while nursing.

A nursing blanket is not required to be heavy or made of any particular material. Many blankets are produced that allow for proper ventilation.

As another poster indicated, they are breasts and not Tupperware.

If she was asked to cover up and refused, I would have appreciated an attendant asking her to leave the plane. She should just be thankful they were not in the air when it happened. I'm sure there may have been other families on the plane, along with children, that Delta had a responsibility for as well.

I would be much more willing to fly Delta if they were readily willing to enforce such a policy.