Degree of Indian Blood

Our granddaughter is half Native American. (The father of the child is Native American. Our daughter is the mother, not Native American) The tribe which the father is a member requires that to be an enrolled member you must possess 1/4 degree blood their tribe. This is where the delay was because the father is not 1/2 of this tribe. We still don't understand how our granddaughter was able to became an enrolled member, but according to the papers we received this week, she is. My question primarily deals with the numbers associated with the degree of Indian blood. For example it says that she is ''13/128 Sisseton-Wahpeton Sioux''. What does this mean? It lists 4 other tribes that the degree of blood was based on, and in the end it says that the total degree of Indian blood is 347/1024. If there is anyone who can help us understand this, it would be greatly appreciated.