Good Day

My mother received notice she owes SARS money after the initial automatic assessment was done. I registered her as an e-filer, and saw that the amount shown as per her pension IRP5 is for the full calendar year. My father passed away in August 2019, and she only received payments from then.

Kindly assist a) is this correct practice that her income reflected is for the full calendar year?
b) What is the maximum income so she does not pay tax?
c) I didn't realise that pensions were taxed?

Many many thanks