MFL specialist here.
pps are pretty much right, the best way to do well is to learn answers in the themes. Yes AQA say they don’t want pre-learned but v few students are likely to be fluent enough to avoid this.
She chooses as @uxo says one of the three themes, and should have already sorted with her teacher which sub themes to cover. Theme 2 is best and ask for qus on holidays and your home - this avoids the dreaded environment and social issues.
Of the other two themes, one is the photo card, which you have no control over (except that it won’t be on your “chosen” theme) - so if you choose 2, the photo will be school or family (better than poverty or recycling).
You get 12 mins to prep the role play plus the first 3 photo questions, then get 2 unknown photo questions which the teacher cannot change.
The order is role play, photo, chosen theme then the third theme not already covered. 3.5 mins on each general theme. So she does need answers on all three themes, but obv will not use them all.
For a tip top mark a student needs to develop all their phoyocard answers and also all theme ones. For a really strong student I would hope to ask a max of four questions on each theme but of course I ask as many as needed to take up the time.
Remind her she has to ask the examiner a question too!