The latest victim lived on a poultry farm in eastern Turkey. The three deaths were the first human fatalities from bird flu outside China and Southeast Asia, where the virus has killed more than 70 people.
Some 25 people are being treated across Turkey for bird flu-like symptoms, according to reports.
The latest victim, Hulya Kocyigit, died early Friday in a hospital in the eastern city of Van. A brother is being treated for the disease, but a doctor told the BBC his condition was improving.
The girl's other brother, Mehmet Ali Kocyigit, 14, died Sunday, while their sister Fatma, 15, died Dec. 29. All four children developed symptoms including a high fever, coughing and bleeding in the throat.