Yes agree, study guides (tho I don't find them wonderful). What sort of grade will she be looking at OP? I mean, is she hoping for 6/7 or will she be happy to gain a grade that means she doesn't need to retake (4/5)?
It makes a difference IMO as if you are aiming for 4/5 you need to think about more basic things such as structure of text, what happens when and why, rather than learning heaps of quotes.
What the examiner is looking for is knowledge of the text - better to have a short quote which you can use aptly than learned a paragraph that has no relevance.
Agree lots of practice questions is the way forward. Look at themes that will come up - eg Macbeth - violence, power, the supernatural, key characters (M, Lady M). Remember she gets an extract (not for Lord of the Flies if it's AQA) so she can use that as a big starting point.
The key to practice essays is explaining and showing the significance - don't just say "Shakespeare uses xx metaphor here" - say why, what effect it has.
Context of the extract is important; there are also marks for context of the whole text eg Shakespeare's audience would have believed in ghosts which make the witches more credible to the audience of the time.
oooh sorry long answer! Lots of other MN-ers know more than I do tho.