I managed to find one for you,

Southern, Patricia (2008). Empress Zenobia: Palmyra's Rebel Queen. A&C Black

But, I believe your best bet for this is not to search for books entirely on her but rather essay collections about Syrian or Palmyrian history.

Cussini, Eleonora (2005). "Beyond the spindle: Investigating the role of Palmyrene women". In Cussini, Eleonora. A Journey to Palmyra: Collected Essays to Remember Delbert R. Hillers. Brill.

Powers, David S. (2010). "Demonizing Zenobia: The legend of al-Zabbā in Islamic Sources". In Roxani, Eleni Margariti; Sabra, Adam; Sijpesteijn, Petra. Histories of the Middle East: Studies in Middle Eastern Society, Economy and Law in Honor of A.L. Udovitch. Brill.