Below is a link that shows the Queen Brahne's final words spoken to Garnet. She states that the all consuming greed she had felt was gone. I always thought that she was inflamed with greed because Kuja put a spell on her. This, of course, is only my opinion but it does explain why someone would change so drastically. :hello:

YouTube - ‪Final Fantasy IX Part 125 - Bahamut's Fury; The Death of Brahne‬‏