I am sticking with the fact that if she can't do it, she can't do it. Why does she automatically just not want to?
Not all women have porn star mouths and not all men have small penises and therefore it is possible for it to just not fit!
But anywho, there is a big difference in putting it into your vagina and into your mouth. I mean if you really think about it you are putting something in your mouth that the guy pees out of. I mean, I have done oral and will do it if the guy really deserves it, but it really isn't the most hygenic thing in the world. It all comes down to everything else that has to do with sex. It is all a personal preference. But, it really isn't fair to say that she can, but just doesn't want to.
I have said it before and I will say it again. I have personally dated a guy whose penis did not and could not fit into my mouth. It really does happen!