the same way you've got her to ...... with you.
black guys aren't special, unless she has a preference for skin color,
I don't see why it would be hard.
If she's flirting with a guy, and he's making moves,
it should lead to them fucking.
If she doesn't want to fuck a black guy specifically, you could see if she'd be ok with a blindfold.
If she's not down, well your ...... out of luck and choose the wrong partner for your fantasy, or dream you wish to fulfil.