Have you spoken to an attorney about it? A letter from an attorney to hers indicating that you are pursuing legal action will make her pretty cooperative, I bet. There is a reason why everyone wants to settle in these matters instead of going to court.
Anyway, I have the same color brows as you I think (dark brown, almost black). I think one issue is saturation. Brow hairs may be that color you are using, but against your skin they tend to be less saturated (gray undertones) since they are scattered and not some solid wall of color. And the overall color from a distance is not as solid/dark as the color of individual hairs anyway. So using the pencil/powder very lightly (or applying it normally and then blotting it off, especially where it tapers at the end) will help with the fake look.
I really wish I could do your eyebrows, just once, because I really think I could make you happier than the way you are currently with your makeup options. 