She received the same salary, but was unaware that she wasn't paying any tax on the top up portion.
This should definitely have been flagged by her employer because in effect, her salary was cut, unbeknown to her. (the difference between her normal salary and what she would normally pay in tax)
She has had a look at her emails, pay slips were requested in October and a few excuses were made (i.e. next week etc..). A colleague had the same request knocked down the road in November.
I'd hate to cry foul or accuse anyone of doing something like this deliberately, but I can't help but feel someone has fcuked up here.