One didn't put reins on a dragon, but Melora rarely rode with them on horses, either. She held on mainly with her knees. If he turned upsidedown he could shake her off, but she could take some pretty sharp turns by shifting the center of her gravity and holding on right. If she flung her arms around his neck, that would be the sign that she feared for her life.
She could definitely tell he hadn't had as much practice flying, yet, but he wasn't bad. If he started to lilt too far in one direction, she shifted her balance to help him correct course. True, she was just a small weight, almost too little for him to be conscious of the movement, but she knew how to get a response from him.