it might be a clogged part of her skin or an inverted nipple nothing more. The black would be oil and dirt that has collected there. Do you have a pic? I have seen them on dogs and a person or two, just a strange place in the skin that has a depression of a sort that enlarges as it collects this oily dirt. IF it is not red or sore i would leave it alone until your next vet trip and inquire about it, you can clean them out but sometimes that irritates the skin around it and they simply fill right back up anyway.