Siona Indians: 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.
FYI, 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!