i had that problem as well she was always like "i don t like it raj" so what i did was stop going down on her. I made her really really wet, kissing softly, playing with her tits, rubbing the clit etc etc and would teas as i was gonna go down on her. Then i would just have sex with her. Few days later she bagged me to go down on her and i said "you get what you give" and yeah it worked fine. Do not pressure b/c females are totally different then us males, more you say ok i don t care they will want to do it more. So i suggest you read up on some more posts or sites. If you are not really really really good at going down on her then read up on cunninglis (speell*) and make her want you to go down her
i hope it was helpful and believe me you are not the only one with this kind of problem many of has been there.