Right! The fight is perfectly doable now if you don't get really screwed over by RNG and initiative, its just nothing tells you on your first playthrough that her getting knocked out immediately ends the fight.
Overall the encounter could be much improved for people on their first playthrough, without even changing the loss condition, simply by:
1. Communicating clearly to the player that Isobel getting taken out will result in some vague nasty consequences (even just one line from your own character saying "If Isobel falls unconscious, the barrier protecting this place will fall" or "all these people will fall to the shadow curse")
2. Either one extra turn after she is knocked out or at least letting the current turn resolve itself.
Its really not much of a problem on second playthrough because you know what to expect, but that shouldn't be an almost requirement for this encounter.
