She needs to do a lot of essays in timed conditions to give herself the best chance of achieving the grades she wants, OP.
For AQA she will sit two exams - each of 2.5 hours. I don't know which 'Britain' one she is taking, but that requires a breadth study of at least 100 years. She will have to write two 25 mark essays based on a 'to what extent do you agree' Q (eg, ‘Financial measures were the most successful means by which Henry VII established his authority in the years 1485 to 1509.’ Assess the validity of this view.)
She will have three extracts to analyse in the 30 mark Q - these are historians opinions and she will need to analyse the argument the historian is making and provide (her own) evidence as to how convincing each one is and to what extent she agrees with them. This is a tough ask.
You have an hour to do the 30 mark q, and 45 minutes (each) to do the other two. It requires in depth knowledge and understanding and an ability to write a fluid, evaluative essay with detailed evidence to back the argument she is making.
For the second exam she will be doing a depth study (Cold War). Again, 2 45min essays and then an hour evaluating three primary sources. These exams are 80% of the mark (20% on an NEA - 4,000 word piece of coursework).
Unfortunately two years work WILL basically be judged on how she performs under pressure on the day of the exam.
You can download past papers from AQAs website. Or ask the teacher to provide them. She needs to practice writing essays blindly in timed conditions.