I think she learned the hard way.
I think it's something like this: 1/25 of her black customers were gang bangers or gave her attitude or something, but only 1/50 of her white customers. So even though 24/25 black customers were respectable people she has decided the 1/25 is not worth it.
I made those numbers up, but if it is something like that, she has cut her rate of bad dates by half, even though in any case it's rare.
I know it's not that she just dislikes blacks or something because she has black regular customers. She just won't see any new ones. Obviously it's that she knows the regulars are good guys so they are OK with her, she just refuses to take chances on black strangers.