We usually have 12-18 months between exams. If she knows the grade she is waiting to do the exam for and is really bored can you ask if she can join the next grade up and start learning that? This happens quite often at our school. Those about to do their exam tend to be at the front then they all change around when the exams are over. It also means your child is getting more classes, but is of course a lot more expensive if they are doing this in every discipline.