Go to the GTS in your DS Pokemon Game, connect to it, search for Charizard with the Female-only option added to it. Note: You have to have Charizard in your Pokedex or you can't search for it. Once you get to the screen where you can see Trainers that have it for an offer. Select one and see what Pokemon you need to trade in to get for Female Charizard. If this helped, then good, if doesn't help, feel free to send a death note attached to a brick through my window and tell me what's the matter.