What Causes Swelling And Difficulty In Breathing Through The Left Nostril?

Hi ! My mother in law is suddenly not able to breathe through left nostril ( her nostril near the eye) is swollen and a little better thru her right nostril. Right now she is breathing thru her mouth. Its late in the night . what 1st aid do i give her till morning ? She does not have a cold but her nose is running now with clear water.