Used Turbotax to submit 1040-SR for deceased Mother in Law 4/29/2021. Followed instructions, included death certificate. Just received a 5071C letter addressed to deceased MIL to verify her identity. Address even includes "DECD" after her name. I do not have previous years' tax returns, and will not go to the web page and set up an account because it says you can only set up an account under your own name. Letter says they won't even process the return until her identity is verified.
What do I do now?