It's best to just keep on fucking her non stop OP. And when you're not actually fucking, rape her mind, make her know that she's all yours. Get one of those remote controlled vibrators. Tell her she needs to let you put it in so you can test whether she's worthy of being your girl, good girls obey orders after all. Then take her to a park or somewhere, go for a nice walk in a public place. When you're holding hands, reach into your pocket and turn it on, starting with the lowest setting. If she starts acting funny but won't say thank you master, turn it up another notch. Maybe kiss her a little bit, bite her neck, you gotta tease her so she really starts begging. She might want you to fuck her now, but, you need to really mind fuck her too. It's the only way to give her her fill. Just keep on torturing her in the cutest ways possible. Dont stop until she begs you to, and even then, keep on going.

See, its more than just fucking the boy out of them, it's putting them in their place, bringing out all their submissiveness and femininity. Making them cum like a good girl is just part of the battle. You need to help them act in such a way even they do a double take and ask themselves "would a real boy ever act like this?" Do everything in your power to make them believe beyond a doubt they really are female. It's a long process but the results are worth it, it's a lot of fun too!