You can't add the 2025 OAS to 2024. You will need to do a final return for her next year.

@Delphision Sorry for your loss. The due date to file the Final Return and pay a balance owing is:

• April 30 of the year following the death (if the death occurred between January 1 and October 31 inclusive)
• 6 months following the death, on the same calendar day as the date of death (if the death occurred between November 1 and December 31 inclusive)

CRA Filing taxes for deceased.

Since she passed away in 2025, you will add that information on Tax Year 2025 not for the Tax Year 2024.

Thank you for choosing TurboTax.