Here are some links on references to 'Siona'.
South America: http://www.glenn.morton.btinternet.co.uk/babel.htm
Langdon E. J. (1992). Dau: Shamanic power in Siona religion and medicine. E. J. Langdon and G. Baer (eds.). In: Portals of Power. Albuquerque: University of New Mexico Press.
Both responses (yours and Pavlov) are right then. I found a site
which had explained Siona as 'graceful'. Janet i.e. Jane means 'grace'
so the site was not too off.
Also Siona is 'warning' in Old Irish.
I am including some links to provide some more background for any
other possible meanings of 'Siona'. Thanks!