I'm nothing to do with the DSA but I would suspect that test routes are for examiners guidance only. They will be at liberty to vary them in case of road works etc.
If there were instructions to stay to a particular course I think more poeple would fail for not following directions.
If she promises to only drive on the test routs and no other roads ever then she should get her licence. The test changed some time ago to stop such people getting a licence, it is no wonder that 1 in 4 drivers crash within a year of their test pass.