Ms Nava had only announced her candidacy for the PRD - the opposition party to President Enrique Pena Nieto - on February 28.
Her son Francisco Quiñónez Nava was kidnapped in October 2012, and a 300,000 peso ransom (£13,000) demanded. He is still missing.
Her husband, Francisco Quiñónez Ramírez, had been mayor of the town from 2009 until 2012, and was planning on making a return in 2015. But he was shot dead in June 2014, when he was driving with his wife near the town.
She was seized by a group of armed men on Monday afternoon.