I really hate to be such a downer but I can tell you from my experience.....that people are gonna think what they want no matter what is told to them! There IS no magic thing to say to open her eyes or to make appeal to her common sense about this.
The best thing is to on with any plans they might have...and let this woman know she is included if she wants to be....if not.....then the loss as all hers.
Sometimes people can change their minds when they can SEE for themselves that THEY were aparently wrong in how they felt. Other people will stubbornly go to their grave with views that are incorrect.
If she stays in Africa.....it may be the best thing for everyone concerned! Sorry to be so harsh...but it's how I feel.....having dealt with bigots for years!
BTW....I wish the best of luck to this couple,