Your assumption is that your doc is a typical Nigerian.
America became strong because (up until recently) the kind of immigrants we got were from the most intelligent and ambitious of the people in the "old country", and they came to the US because they felt that their talents would be better rewarded here. Now we're also getting people who want to take advantage of the welfare and social service setup. Your doc sounds like she's in the former category
There are also plenty of intelligent and energetic American blacks. Look at Clarence Thomas, Alan Keyes, Thomas Sowell, Walter Williams, etc. They just are too smart to spend their time hanging out on porches in bad neighborhoods