Police said she blew herself up on a major Shia religious pilgrimage route in Iskandariya, 40km south of the capital.
The attack came a day after a bomb killed eight people in the southerly Shia holy city of Kerbala.
Hundreds of thousands of pilgrims are heading to Kerbala to mark Arbain, one of the most important dates in the Shia religious calendar.
The Arbain rite marks the end of a mourning period after the anniversary of the death in the seventh century of the Prophet Mohammad's grandson Imam Hussein.
The attacks occurred despite heavy security on the pilgrimage route.
