Ann Marie De la Houssaye, 37, of Vallejo, was arrested on suspicion of elder abuse and neglect and possession of a controlled substance, Lt. Sid DeJesus said.
Solano County Health and Social Services asked police to check on the welfare Tuesday of 78-year-old Rosie Dright at her home at 148 Florida St.
The Vallejo Fire Department also responded, and police found Dright's body in the home. She appeared to have been deceased for "a lengthy period of time," DeJesus said.
Health and Social Services officials identified De la Houssaye as Dright's care provider, DeJesus said.
She was booked in the Solano County jail.
The Solano County District Attorney's Office filed misdemeanor complaints Dec. 18 and June 13 against De la Houssaye, according to Solano County Superior Court records. She was scheduled to appear in court Oct. 7.