Ross died on March 12, 2013, leaving Rachel, his wife, and Emma, their daughter. Emma, who turned 20 in 2018, is a part-time college student and continues to live at home with her mother. Rachel provides 65% of the support for Emma. Emma works part-time and earns $3,650 in 2018. Rachel, still grieving over the loss of Ross, has not remarried. What is Rachel's filing status in 2018?