Sarah and the final neighbor took the wrong amount, which means that 15 neighbors – 1 Sarah – 1 final neighbor = 13 neighbors took 10 cookies each.
This is a total of 13 neighbors * 10 cookies = <<13*10=130>>130 cookies taken by the first 13 neighbors.
There were only 8 cookies left, so that means the first 13 neighbors and Sarah took a total of 150 – 8 = 142 cookies.
So Sarah must have taken 142 – 130 = <<142-130=12>>12 cookies.
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