I think the real key is why did she cross the 'portals'. The statement from the helo pilot gives some clue that he could see light through the gap. This is probably what the Islander pilot saw as well, bit of light, the mistaken belief that beyond the saddle was wide open clear air, combined with the web cams at Bathurst Harbour showing OK conditions once she had passed that point. After crossing that saddle and it closing in behind then there are very few options, so in a way its a critical location. She obviously tried south, then north to no avail and then tried to get back through the saddle. Once she had crossed the 'portals' her fate was sealed, that is the critical point in this, from there she was trapped in a weather bowl with the choices being land on whatever suits or try to fly through some bad conditions to freedom.
The point here is that if flying through tight spaces, make sure when you pass critical locations that you are certain that the path ahead is clear and that the pass behind is not subject to rapidly closing. I think here the idea that there was multiple options to use after the portals gave the pilot some confidence to continue through a very small gap and then found out that in some rare circumstances all routes out of the next valley become blocked.