ca. 1571 Eleonora di Don Garzia di Toledo di Pietro de' Medici by Alessandro Allori (Kunsthistorisches Museum - Wien Austria)
Thank you wuvums for providing the correct name for this lady and lifespan dates that can be used to approximately date this portrait! (Input provided on 8 November 2008 when the next image was posted on Webshots.) This image of Eleonora di Garzia di Toledo, who was raised by Eleonore de Toledo, wearing a dress showing Spanish influence is often called Maria de Medici. Her Wikipedia article is here.
The Wikipedia article for Alessandro Allori is here.
Upgrade image from Wikimedia posted on 23 January 2013.