Well, her parents never thought that she would be able/willing to wander off into the jungle alone.
Hmm.... key events:
They leave the British Isles to go on vacation in Malaysia
After they get checked in she disappears.
6 days later she dies.
3 days after that her body is found.
The key question is... where was she? Wandering in the jungle for 6 days in which you eventually end up 2.5 km from where you started is not a major athletic feat... especially in a jungle with foot paths created by regular hiking.
The medical report showed that she died of injuries related to hunger. The initial investigation got ruled "misadventure" because there were no signs of foul play. The ONLY thing that was even out of place in their lodging was a window left open.
It still leaves the question of how searchers didn't find her until 9 days later though.
Scent dogs.. well... they're not guaranteed to work, useful tool, but not a given, and dense jungle is pretty much the best way to hide from IR cameras.
One thing pointed out by the initial investigation team, is that, while the mother claims the girl was weak and sickly..... CCTV from the airport shows her dragging her suitcase around the airport. So the Malaysian officials investigating concluded if she's healthy enough to carry her own luggage, she's healthy enough to hike in the rainforest. The question of if Nora would have been willing to do that barefoot and nearly naked is another matter.... and one the mother hotly disputed.
But well... there's no actual physical evidence that contradicts the idea the girl just went on a walk and got lost. It's noted that she was found on a stream bank in a location where she might have been drinking water because she was thirsty.
The current ruling is simply that "we don't know enough to say what happened."