I am very sorry for your loss.
A 1099-C is a form a debtor sends when they cancel a debt. The canceled debt is considered income.
Considering your husband passed away in 2016, you cannot do a joint return this year. Therefore, there is not a return to add the income unless there was an estate opened. If there was no estate or probate opened or the estate was closed, then there is nothing you can add it to. If you want to be cautious you can put "deceased " on it and send to the IRS with a letter or you can address it later if they contact you over it.
If you are on the 1099-C as a joint recipient of the canceled debt, you need to include it on your return.
