Her stench is Zodiark, patron deity of the Ascians, of that I am quite sure. We have had no reason given as to why Shiva and Gaius would have met so they probably have not but we do know Gaius has been working with the Ascians of which could of brought Gaius into contact with Zodiarks taint/corruption. Regarding the 'she' part, much like Hydaelyn's voice is female my belief is both Hydaelyn and Zodiark are female as they are probably two sides of the same coin metaphorically...a single entity once upon a time that split in two separating into light and dark so if Hydaelyn is female then so would Zodiark be in my opinion.
http://img2.wikia.nocookie.net/__cb2...rk_Crystal.png