It appears she made the first move on the subject and most likely wants you to approach her about it.
I will say though only do it if its what you want and make sure your relationship is water tight before you make the plunge because once that seal is broken she will become a changed woman. Talking from experience here.

If you don't let it happen she will always regret it and hold it against you. However understand if she is with the right black man she will never be the same. If it was with me, I'd let you be present and follow your rules the first time. But the next time, and she will desire a next time, we will be alone and she will willingly follow my rules.

Absolutely you should without question. However, "let" is the wrong word. You should "encourage" her to cuckold you with black men.