Was on the third floor pwr leveling my lvl 35 shammy with my lvl 72 bard - she appeared in the far right room where the shadowbeast cook is located and needless to say wiped my **** (had to fade with bard )- didnt even know who she was until i looked her up here - what normally makes her spawn? i guess whatever it is I did it without knowing
This is a version of Tserrina that, far as I know, have existed only once; during the Save Firiona event, which pre-dates your post by years. The normal Tserrina is alot easier, and should have been easily doable by a 72 bard; I've heard people mentioning her spawning on any of the floors which has bats in them.
I don't know exactly what you encountered, but I find it hard to believe that it would be this Tserrina version, unless Sony made a horrible mistake during a patch at some point.