Unfortunately this is a result of how the rules for Vehicle Excise Duty have changed over time. If your daughter is paying zero road tax it is likely that her car was registered between 2001 and 2017, when the rate of VED was calculated solely on CO2 emissions, with cars emitting less than 100g/km eligible for the zero rate. Since 2017, only vehicles emitting less than 50g/km of CO2 are eligible for the zero rate, while all other vehicles pay the same £190, or £180 for alternative fuel cars such as hybrids and plug-in hybrids.