She's had a tax demand for underpaid tax. She's a pensioner on about 11k a year pension, hasn't worked in 4 or 5 years.
It sounds like they have her old employer an incorrect tax code so they weren't deducting enough at source. She's writing them a letter saying she can't afford to repay it and she thinks its unfair that they're chasing it when its their fault. What are the chances of her not having to pay it?