First of all, you would've gotten a much better response from the author if you had said that you didn't think these disparities were Black people's fault, and that you were in favor of equalizing resources. Most people who cite these facts use them as arguments against giving Black people more resources, and blame black people for these disparities.

Your argument has become subtler as you have refined it, so you have arguably managed to evade some of the author's objections. But I think she is still right that the Nigerian example doesn't prove there is no Anti-Black racism in the USA.

For one thing, there is some evidence that there is more prejudice in the USA against African-Americans than against immigrants from Africa. White People are less like to fear a black face if it has an African accent.

Also, the Nigerians in America are better off financially than most WHITE people in the USA. As the author points out, most Nigerians in the USA got here because of their connections to well-off and well-connected families. Consequently, they can do as well or better than the white families in spite of encountering Racial prejudice. Your argument thus doesn't prove Nigerians don't encounter racism. It just proves that the effects of the racism can be counteracted by money and connections.