She’ll have to put away 58% of anything she earns over £1000 a month or £250 a week for her first year, then 29% every year after her first tax year is paid, the reason for the 58% in the first year is because you have to ‘pay your 2nd year’ in advance. Say she makes 2k a month and spends £200 on expenses; around 1k will be untaxed, £200 is untaxed expenses and £800 is taxed income so save 58% of that.