I have wondered the same thing. If I had to guess I think it is her personality, I think she has a great personality and also has a genuine interest in fashion. I think the designers and backstage people like her.
The personality angle is the most overrated and glorified answer in regards to any model with questionable longevity.
It has a lot to do with her connections. She's with one of the most powerful agencies in the world that thrives on public image and even though she's no commercial cash cow, Hanne sort of has a pseudo-cult image that's popular with "the cool people". She's big on the social scene (not the elitist side though) and she's a street style favourite.