To get it reassessed with the new income , she’d have had to file a T1 adjustment, with a new T4/Amended
If she receives the money in 2023, as back pay due to a raise , for 2022, it’ll be reflected on their 2023 T4, hence 2023 tax return
“ Income is reported on a T4 slip for the year in which it is paid, regardless of when it was earned“
Example . I’m getting salary adjustments from 2020-2022. It’ll be reflected on my 2023 T4
https://www.canada.ca/en/revenue-ag...mation-employers/t4-slip/filling-t4-slip.html