But when the family went to CHOP to discuss the transplant, Rivera said she "thought we were just finding out how transplant works and how we could be a donor."
"But then, I was told we couldn't because she was mentally retarded," she said. "Those were the exact words on a piece of paper."
Rivera said the doctor also mentioned the medication that Mia would have to take for the rest of her life and "how important it was she take it -- and who would make her take it when we weren't around anymore?"
"Everyone should be treated equally," she said at the time. "This is outrageous."
Rivera also argued that medical information about the syndrome was "out-dated" and there was "hope" that Mia could well benefit from a kidney transplant.
At the time, CHOP responded to the outcry on its Facebook page: "We hear you."
Other medical ethicists defended CHOP, suggesting its decision was not based solely on Mia's disability.
"It is appropriate to decline to perform transplants that are medically contraindicated, but denials based solely on the presence of mental retardation would be a throwback to the practices 40 years ago when Down syndrome children were frequently allowed to die for lack of treatment of correctable conditions," R. Alta Charo, a professor of medical ethics at University of Wisconsin, told ABCNews.com last year.