I think it's a continuum. You are higher contrast than somebody like me...but lower than some others. (I am not sure who told you that you were medium contrast -- do you agree with the assessment?)
Deborah typically wears all black -- which itself provides high contrast to her fair skin and hair. It works on her because of her personality, and because she is intentional about it. She doesn't just throw on some black stuff without any conscious deliberation. She adds lipstick. She is perfectly groomed. She defines her brows. (This is HUGELY important for fair haired people who want to do high contrast, IMO -- either that, or wearing dark framed specs.) She often adds shine (and light) in the form of silver. This works.
Deborah more rarely wears black with white or ink with white. This also works on her for the same reasons. It's styled. She wears it consciously, with thought. And it's dramatic, which is what she is aiming for.
If she wanted a "harmonious" look with her fair colouring (less dramatic) she would wear lighter tones that are not so light as to wash her out.