The fight is pretty simple (I did it twice on hard difficulty already, without any problems). The idea is to charm one of the minions (not the dragon :D) and then incapacitate the dragon as well as you can (you best have a mage with INT 25+ to do this) while hacking away. Blind and Stun works especially well.
Astarte's an idiot. You best have an active healing spell on her all the time, otherwise she'll just die on you. If possible, take her out with an AOE stun or something.
