Anyone still 16 after the last Friday in June (the date the law assumes compulsory schooling is over) is allowed to work as late as 10pm, for up to eight hours a day, for up to 40 hours a week. She is entitled to a minimum wage of £3.57 an hour, and you must provide a 30-minute break every four and a half hours. She is also entitled to paid leave?.
Be very careful about taking on your neighbour’s daughter as a favour. This really needs to be a hard-headed business decision. You’ve got a licence to protect and, however sensible she is, you’re going to have to double check virtually every transaction she makes.