I think the most common strategy will be to stick her in the sluttiest outfit and just leave her that way all game.
[SPOILER="Probably one of these two."]
[Image: http://images1.wikia.nocookie.net/__cb20130917184937/finalfantasy/images/5/58/LRFFXIII_Soceress.jpg]
[Image: http://images1.wikia.nocookie.net/__cb20130718045412/finalfantasy/images/2/2f/LRFFXIII_Miqo%27te_Outfit.png]
[/SPOILER]