Sometimes, animals sense that something is wrong with one of the babies and will try and kill it and only it....maybe she would raise all the others just fine. I think I would give the little guy a friend and give the mom back her babies. But, watch closely to make sure that she doesn't go after any of the others...
Great advice. Wish I had had more than 3 chicks, this would have been a great solution. She was such a good mom to the other 2. I didn't mention that she killed the first black chick and this one was a replacement. She definitely had it in for non cream colored chicks. So weird.