Not sure what you are getting at. To calculate the percent of the DNA contribution of one 8th generation ancestor requires only dividing by the number of 8th generation ancestors. This is 1 over 2 to the 8th or 1/256. Considering only female ancestors or adding the 2nd through 7th generations ancestors to the formula does not help. The 2nd through 7th all got their DNA from the 8th.
Wrong! There was no exact generation reported for her suspected “Indian” DNA. It was a range of generations, and so the original “Indian” ancestor would be one of 992 possible persons or approximately a 0.1 percent chance that she is part Indian, assuming that her DNA from Mexico, Peru, and Colombia is actually Indian DNA.