A woman set on fire, allegedly by her ex-boyfriend, has died of her injuries, authorities said Tuesday.   49-year old Deborah Prater was pronounced dead at UAB Hospital, two days after the attack at her Edgewater home.  The sheriff's office was expected to upgrade the charge to murder for 48-year old Michael Kennedy of Mulga, and request that his bond be revoked.   Investigators say Kennedy has a history of arrests dating back to 1995.   He is also a paranoid schizophrenic, authorities said.