It happened on Deverney Road in Omagh on Saturday, August 18.
She has been named as Kyra Elizabeth McKinley.
The collision involved two cars shortly before 10 am.
The Deverney Road was closed for a time at the junction of Tormore Road and Edenderry Road but was re-opened.
Police are appealing for anyone who was travelling on Deverney Road around the time of the collision and who witnessed anything, or anyone who may have dash cam footage of the collision to contact local officers in Omagh or the Collision Investigation Unit on 101 quoting reference 523 of 18/08/18.