Apprentices under 19 years are not entitled to receive the National Minimum Wage.
Apprentices aged 19 and over, who are in the first year of an apprenticeship, are not entitled to receive the NMW.
As your step-daughter no longer seems to fall into either category, she is entitled to receive the NMW of £4.83 per hour. So her gross pay should be £198.03 per week, with take home pay of about £173.64.
Chris
PS: I've no idea what Dot is on about. Unless their contract specifies it, nobody is ever entitled to receive a higher hourly payment for 'overtime'. As long as their average pay, across a 13 week period, meets the NMW there is no automatic entitlement to ANY pay for overtime. (Junior doctors are only paid at one third of their standard rate when they work overtime).