Fraser police say they were called to Richard's Middle School on Wednesday afternoon after two parents got into a fight.
When investigators arrived on scene they found the fight had ended and one person allegedly involved in the argument had left the area.
Witnesses reported the parent who left had been assaulted by another woman during a confrontation about parking.
Officers spoke to the other woman involved, 43-year-old Lisa Rosales, of Warren, and determined she was highly intoxicated. She admitted she had driven to the school to pick up her 13-year-old daughter and had been drinking alcohol.
She was arrested for operating while intoxicated. She was also in possession of marijuana and oxycontin, which is not prescribed to her, police say.
Rosales submitted to a breathalyzer and it registered .18, well above the legal limit of .08.