I had wondered if it could be accumulated dirt due to her not taking it out when she washes her face that we're only now seeing due to her new camera, but bruising due to the blood thinners would also make sense. How difficult are the hoops to remove as opposed to the corkscrew studs when you have beetus paws like Amber's?
EDIT: Actually, now that I look at that picture again, it looks like she's got a dark spot on her other nostril as well, just not as dark as the one with the piercing. Can get you acanthosis nigricans on your nose?