Vanille's second ability checks the battlefield at the moment it would trigger to see if you own and control Vanille and a creature named Fang, Fearless l'Cie. If you don't, the ability won't trigger at all. If it does trigger, the ability will check again as it tries to resolve. If you don't control both Fang and Vanille at that time, the ability won't resolve, you won't have the opportunity to pay {3}{B}{G}, and none of the ability's other effects will happen.