Hi OP MFL is my subject. Is she in year 11? If so the best thing is to practise the actual exam she will be doing.
Assuming AQA, there should be three sets of past papers - sample, 2018 and 2019, which is now generally available. even if she has done these for a mock it is still worth looking again.
She needs to do the paper, then see how she did. Then look at the transcript of what was said and see where she went wrong. Is it about lack of vocab knowledge, picking up a word when it's the wrong one, mixing up meanings or falling for false friends?
They are sneaky in that they often mention all the possible answers in the text. So she needs to watch out for negatives or refs to someone else etc.
I would also look at the mark scheme as there will be things that are not acceptable - eg the French word for kind is gentil - but "gentle" is usually specifically not OK as an answer.
Once you have exhausted all the past papers, it might be worth looking at another board - Edexcel also do MFL GCSE; and there are legacy papers if you hunt online from before the GCSE change which will still be useful in terms of audio plus questions, as long as she remembers that the format of her exam will not be the same.
There are also CGP workbooks - I don't think they are amazing for listening but better than nothing. HTH.