Having dealt with my mother's last filing, knowing Social Security monthly payments cover the previous month and with COVID things are still not back to normal in their office, the best thing is for you to contact Social Security to advise them you have not received the SSA 1099 for this year. Knowing your mom is deceased, they should talk to you and send or resend out the SSA 1099 for taxes. Since it is the last tax and stating deceased after her name, it's best to report exact amount on 1099 for peace of mind. At least that's how I would feel.
Best to you.
