What Causes Umbilicus Odor With Discoloration?

Yes...I want to help my best friend Kellsie but don't know how And most sites I've looked on hAvent gave me any good answers. She has a REALLY foul smelling odor coming from her belly button. She said she cleans it out with q-tips but nothing helping. Example yesterday she said she cleaned it thoroughly and within 4 hours she checked it again and it was already foul again and shed also noticed brownish color now on the q-tip. She said that was the first time that happened. That usually there's no color..,I told her determined to help her get rid of it...any ideas on what it could be and how she can stop it/prevent it???