DigMe, the guide wasn't charged with "reacting badly", and of course there is no such law. In fact, the story was badly translated. According to the original story in Norwegian, the guide wasn't charged or fined at all. The company she works for, a Belgian tour operator, was fined because they hadn't trained and equipped their employee properly...
It is legal to shoot a polar bear in self defence, they won't let you out in the wild up there unless you have a gun. But because the bears are protected, you can shoot only after exhausting all other options, like leaving the area (snow mobile, boat) or scaring the bear away. Flares and flashbangs almost always work, as do dogs if you have them. The guide in the story above did for example have flares, but failed to try them.
I saw a TV program a couple of days ago about polar bears. A Norwegian photographer visited a Russian biologist on Wrangel Island in the Arctic Sea off Eastern Sibiria. This being Russia, no guns were allowed. This biologist had never carried a gun around polar bears, he used a big stick instead. I'm not kidding. The two of them video taped each other as they did things like walking to the outhouse, frequently having to chase bears away. This was done by yelling and waving their arms and a long piece of driftwood. If the bear didn't get the point, they would hit it across the nose as hard as they could. Just imagine a bearded Russian in a fur hat running after a 1500 pound polar bear, shaking a broom stick at it.
Seriously, this biologist had spent several months at the time every year for ten years studying these bears, I think the highest number he said he had counted around the cabin at one time was 160 bears. Of course, working in an invironment like that, a gun is useless anyway, unless you want to exterminate the wildlife you came to study.