We can just speak in general terms without more information.
Has she checked the time clock next to the meter?
If her heater is coming on an hour early automatically, it is likely she is being charged at the night rate an hour early as the time clock is ahead by one hour.
Does she have one meter which clocks day and night separately or does she have a regular meter and a night storage heater meter? If she reads the meter or meters or 10pm and again at 11pm, or the following morning at 7am, she will be able to see if where the units have been charged. If they are charged on the night rate or the night storage heater meter, she is being charged the lower rate.
If you have any other questions, please don't hesitate to ask.