@sjw
Just thought of something... what if there's something about that kitten's smell that makes the mom think it's carrying a disease, or is ill, and it's trying to separate it from the healthy ones?
We've seen in the past cats develop maternal instincts towards birds and rodents, so I don't think it's just a racism thing. And presumably the kitten came out of her, and carries her smell just like the rest of the litter. Unless... something bad happened to that specific kitten.