Ellen Harvelle was a retired hunter who ran a saloon called Harvelle's Roadhouse that her fellow hunters often visited until it was destroyed by demons, at which point she resumed hunting.
Ellen hunted with and was married to Bill Harvelle prior to his death. She and Bill had a daughter named Jo, who later became her hunting partner.
Her life is pretty much identical up until Supernatural's fourth season.
Ellen Harvelle investigated the murder of Ross, the latest in a series that had been taking place throughout the last ten years. She questioned Ross' girlfriend, Liz, before finding Jo who had come to do the same thing. Liz told them that Ross' mother and older brother had also been killed. Together, Ellen and Jo learned that Ross' father, Steve, had been with a girl called Sarah Black, who hanged herself and became a Banshee. She had been killing Steve's family in revenge for him dumping her. Ellen and Jo confronted Sarah who overpowered them before being killed with a golden blade by Amy, a demon that Jo had earlier encountered. Ellen tried to kill Amy but she escaped.