CatherineCawood for your DD's sake, keep her away from the Student Room post-exam analysis! It would make anyone convinced that they have failed, even if they later turn out to get 100%.
Sost I suspect your DGD did a lot better than she imagines. She knows her stuff, and she's a sensible girl, so she'll have put together a practical that uses all the scientific thinking that she's been learning for the last two years.
About exams not covering what you've revised, wasn't it always this way? Unless you know absolutely everything (and who does?), you always go into an exam hoping that what you know comes up and what you ought to know, but don't, doesn't.