My girlfriend..

Okay so me and my girlfriend have been together for a long time now...I havent had enough balls to bring up that I want to see her take a BBC. Im worried to how she will react...She just doesnt seem like that kind of girl, and shes kind of shy. She has let me take pics of her once or twice before and has taken pics for me. Even when I wanted to post the pics she declined and said that the pictures are only for me, but I think its more so shes self concious about her body? I have asked her before if she would be down for a threesome, or me and another guy tag team and she said said "no way!" Im just wondering if anyone else out there has had the same thing with there wife/gf but eventually she ended up doing it. Does anyone know a good way to bring it up? or test if she might want too? I once made 2 fake pictures of her taking a black cock and sent them to her...she didnt say much other than " how did you do that, looks so real"....i wish she would just take some BBC!!!