No, you can't ask anything about the paper in the exam. I tell my youngest pupils that if they can't immediately understand any of the words in the questions they should keep calm and try to work out what it means from the context - this is usually possible. I think that more child-friendly vocabulary is used nowadays (certainly in the lower-grade exams) than used to be the case.
I remember my son coming out of his Grade 1 theory exam at the age of 6, saying that he didn't know what 'statements' had meant, but had guessed - the question was along the lines of 'Which of these three statements is true?' - so even if you take the word out completely it still makes sense. Another unfamiliar word was 'omit' in his Grade 2 theory a couple of terms later!
As others have said, though, a 12-year-old shouldn't be having such problems with vocabulary - although I have to say that nowadays it doesn't surprise me - and don't get me started on SPELLING

!! I suggest that you make a list of the words she is unclear about and just get her to learn them as part of her theory work.