Audrey,
Do you know why your mother wasn't treated with ATG initially? Unless there's a contraindication, it's almost always the first-line treatment for newly diagnosed aplastic anemia patients.
Given the unclear advice from your mother's hematologist and nephrologist, you might want to see another hematologist for a second (third?) opinion. Have you spoken to
Dr. Charles Parker at the University of Utah School of Medicine? He's a known expert with a focus on aplastic anemia.