That's great then, sounds like she's Heading in the right direction. Now she needs some gentle, non pushy encouragement and support. I take it that when you say she's becoming more open to the idea, that she knows how much you'd love to see her take a big black cock? If that's true and she didn't freak out or shoot you down straight away, then that's a very good sign that she's at least interested in taking this further.
The hard part for you now is not to get too excited and push too hard and back her into a corner. If it can be her decision to find a black guy to fuck her so much the better.
In the meantime, the bbc porn seems to be having a positive effect on her.
I wish you lots of luck and hope you get there and that she learns to love black cock as much as I do xx