She has a point about 'zones'. People do keep to zones. Largely. Of course there is some overlap, but name me any city without different parts of it where you will find predominantly black people, predominantly white people, predominantly asian people... etc
I've seen it. We went to visit family and friends in London and they all lived in areas where there were lots of people from the same country/of the same ethnicity (in our case black. Kenyan. Kikuyu.) It is bonkers to try to deny that this happens. People (not everyone, but enough for it to create a visible effect) go to where there are others they perceive to be 'like them'.
What we need, instead of denying this happens, is to find out WHY it happens. And see if it needs changing, so that people don't feel the need to seek out others like them and create a community within a community.
Do people feel afraid outside of the familiar? Is it economic? Is it about convenience? Is it an unthinking action? A belief that this is 'your' area? Is it about feeling connected to some over others? Feeling you share something?
People do do it. That is an undeniable fact. What is interesting is why. And if something could or should be done to make people feel differently.