As mentioned elsewhere, the journal article on which this is based specifically found that the difference in rates among women was not significant enough to make a statement about women arrest rates based on race. So the data provided in this article are based on a restricted sample size and it is challenging to make statements about the overall population saying that "white females are arrested at a higher rate than black females". That might be true but we simply can't be confident in saying that that is true unless more data is gathered. Speculation on why such a difference could occur is harder still.