Sick chicken! Help!
Nasal drainage is a sign of a respiratory disease such as MG, ILT, bronchitis, coryza, and others. I would check her for tiny bugs on her skin around the vent and elsewhere which could be lice or mites. Is her vent area dirty from having diarrhea, or is she just generally dirty? Does she have a bad odor around her head? I would clean her off, and check her eyes for foam or pus. Is she sneezing or wheezing? Here is a good link about the common respiratory diseases and symptoms: http://edis.ifas.ufl.edu/ps044