Brake wear

[Deendog]

Morning
Sister just took her car in to dealer re grinding noise from rear. 2013 RRS 18k miles. No warning lights.
Rear pads down to metal. New disks pads and sensor required.
Her driving is mixture of B roads dual carriage way etc
Dealer explained only one of the 2 pads has a sensor so if 'wrong' pad wears out no indication will be given on screen.
Car was serviced in jan 14 when rear brakes were described as 'half worn'
They say 12-18k normal life of pads and she should have checked them rather than relying on sensor.

Does this sound normal?

Thanks

[Deendog]

Agree. I wondered whether calliper had been sticking on. The wear since jan service seems excessive