She played the role of The Mother in Director Matthew Mishory's debut feature, Joshua Tree, 1951: A Portrait of James Dean.
Daniels was born Erin Cohen in St. Louis, Missouri, where she grew up. Her father was an Architect and her mother was a clinical social worker. She grew up in a Jewish family; her mother co-founded the Central Reform Congregation in St. Louis and her grandmother received an award from the National Conference of Christians and Jews. She attended Clayton High School and Vassar College, graduating from the latter in 1995 after majoring in art.
In 2002, the St. Louis Film Festival awarded Daniels the Emerging Star Award. She appeared in One Hour Photo, Wheelmen, and House of 1000 Corpses before becoming a major cast member of Showtime's The L Word. Her depiction of Dana Fairbanks on that show prompted an anonymous donation of a million dollars to the Dr. Susan Love Research Foundation, an organization that promotes and funds breast cancer intraductal research.
Daniels married Producer Chris Uettwiller in 2008. They are currently living in Los Angeles with their two children; a son born 2009 and a daughter born 2012.