She didn't redefine them. As someone[0] linked upthread (which you should have seen if you're down here) racism has a sociological definition as well as a colloquial definition. A dictionary does not define words; it records their common usage. It is, by its very nature, out of date.
Regarding your example of white people in areas with a higher black population, it doesn't quite work out. Almost any other environment, you have the advantage being white. A black person doesn't have the same luxury. They can't scoot away and suddenly go back to being privileged.
> "the oppressed cannot, themselves, oppress their oppressors"
Let me re-define the concepts that tell you are story. But you can't argue that I am telling you bullshit because I redefined basic concepts.
But ok, let's adopt her definition. There are situations based on places, times, locations where black people outnumber the white people (could be a certain organization, a club, workplace, street, city). In that case she is dead wrong as the oppressed oppressor labels get reversed. But you know what this is mental gymnastics bullshit.
Most people have a basic definition of racism. Redefining the terms to support her stupid comment -- smacks of dis-ingenuity.
> dragging this tweet out as evidence of her hypocrisy smacks of willful ignorance.
So is doing complicated mental acrobatics to support her.