I don't think she discusses that much, and if she was so vehemently anti-Cocoon I'm surprised she didn't try to kill Lightning and the others. She was only really against Cocoon during the war, which seems understandable enough. Really, Fang and Vanille were pawns used by the Fal'cie to be used in war. Bear in mind they both end up saving Cocoon from annihilation.