After it finishes casting its hellballs, all she does is stand still. No fightning or anything. She will chase you though, but that is it.
Also, there is a faction bug tied to attacking the dragon. ALL of the guards in Tel were hostile, and the Snipers in Nagritch were also hostile. (not the guards, just the snipers) Unless of course it was intentional.
If this has to many spoilers or anything, just delete this off and send me a PM.

Thanks,
-Darkfire