These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Judging by Bethany's account of her recovery, this seems to be a case of Reality Is Unrealistic.
Which doesn't mean Ebert's (and other critics') problem with the movie is entirely unjustified, either - reality often doesn't make a good story, and filmmakers need to know when to diverge from reality to make the story more engaging.
Nausea Fuel: The shark attack scene and the stump can be this to some.
Special Effect Failure: Sometimes the length of Bethany's stump changes throughout the movie.
The stump was gotten by photographing AnnaSophia wearing a green sleeve on the relevant arm and then erasing that arm in post-production. The real bite was almost up to the shoulder.
The shark.
Tear Jerker: If you don't get choked-up at least once during this movie, you have no soul.