Free tuition for private school

Dear tutor,

Why this free payable of tuition fee (otherwise she has to pay £4,600) is not taxable? As per law, only workplace nursery service for childcare is exempt benefit. Besides, this is her granddaughter, not her daughter. How can it be?

“Between 6 April and 30 June 2023, Diana’s granddaughter attended the private school operated by Patience’s employer at no charge. The standard tuition fee for this period was £4,600, while the additional marginal expense of providing the place was £540.”

Can you please enlighten me?
Thank you in advance!