Sorry for your loss.  Did you notify the Social Security Administration of their death?  Before you file a decedent return, make sure the Social Security Administration has been notified of the taxpayer's death. You can either go to their website or call 1-800-772-1213.

Can I e-file a tax return for someone who is deceased?

https://ttlc.intuit.com/community/e-file/help/can-i-e-file-a-tax-return-for-someone-who-is-deceased/...