An ancient light or sun goddess or some sort of cosmic entity. She is married to or is the significant other of Thunderhead
In 1996 she was captured by humans and her disappearance led Thunderhead to attempt to destroy Astro City, blaming them for her disappearance.
Presumably, she has some control over light. Since light is often associated with the sun, she may also have power over plants, growth, and fertility as well.