All most all woman that dont do it is because they are insecure about it. Some feel stupid because they are not secure with themselves when it comes to sex. My bet is she also just lays there when your fucking her. Your job is to make her feel very secure when fucking around. Talk dirty with her and have her do the same. it might take awhile but she will surcum to it. Watch alot of porn with her. And when she does go down on you, tell her how good she is at it, no matter how bad it is. Bad head is better then no head. And then work with it. Also jump into a sixty-nine position for 4 play, she will be forced to do it and wont feel as insecure because you are not staring down at her and pulling her hair. Its time to teach and a student can not improve with a bad teacher. Its up to you!