She doesn't pay every penny of her fortune in tax.
She is domiciled in the UK, which means she pays UK tax.
How much tax she pays is a complete mystery.
As a simple example, on PAYE, as a salaried worker, you will pay 47% tax on earnings of say £10 million.
But using a personal services company, the tax rate is 23%.
It would make more sense to follow the latter route.
Nobody sets out to maximise the amount of tax he pays, and what her overall tax % has never been published.
Perhaps she feels that it is reasonable, but under tax regimes of the past (e.g., 80% in the 60s under Labour) she would have felt otherwise.
She has stated that she is UK domiciled for tax purposes and doesn't mind paying tax. How much tax she pays, or if her accountant minimises the burden, is not known.