FILING OF INCOME TAX RETURNS - Income Tax

My client is the wife of deceased bank Manager who expired during November 2019. She received the death benefits of her husband to the tune of Re.1 crore. She did not file any return. The Department issued notice during March 2024 showing her fixed deposits in the bank and the said amount has escaped assessment. She filed reply through her auditor attaching the death certificate of her husband, the certificate of employer's showing the details of death benefits which are almost exempted. It was requested on the basis of the documents to withdraw the notice. When this matter comes to me I arranged to file the income tax return for the AY 2025-26. But the income tax return for the previous years could not be filed. What is the remedy in this case?