My 15 yr old have brown liquid running from her nose?

May be serious: Running fluid from nose is usually clear mucus, often associated with a Head cold. The fluid can turn red or brown if there is any blood in it. This change could be due to infection or inflammation often caused by a virus. Such afflictions go away in 5-7 days. if it persists or worsens, go see your PCP or an ENT doctor for medical check up to find the cause and for treatment..