Izzy Powell suffered from Hemophagocytic lymphohistiocytosis, a disease in which white blood cells can build up in an organ and destroy other cells. Her liver had become so enlarged it caused her ribs to break, according to the family.
She leaves behind a twin sister as well as an older brother.
"She fought until the end and squeezed my hand tight until she left," parents Allyson and Landon Powell wrote on Facebook. "My heart is broken, but I am blessed to know she is healthy and whole in heaven. I like to think she is twirling around and singing."
Powell, who spent three seasons as a backup catcher with the Oakland Athletics, signed with the Mets earlier this month on a minor league contract. He is active in raising awareness for the need for organ donors because of his own battle with a liver disorder -- autoimmune hepatitis, which requires him to take medication daily and which may cause him to require a transplant later in life.