I have the Dark Bordeaux GST, so obviously I'm partial to that color. If your mom tends to wear black or neutral-colored clothing, I'd say that she should get the Bordeaux, especially since she has other black bags. If she wears a very colorful palette (e.g. pinks, oranges, greens), then she should stick with the Black.
The Dark Bordeaux is gorgeous, and gives a fresh twist to the classic GST.
-Stephanie (pond23)