Social Security taxable

You indicate that your wife did not file for Social Security until this year.  Thus, it appears that her account was not opened last year and that no Social Security income was deposited into her financial accounts during 2018.  So you should not get an SSA-1099 for 2018.  Next January, you should expect to receive a 2019 SSA-1099.  That SSA-1099 should show the net benefits received in the colored box number 5.  It will include benefits for 2018 and 2019.  Next year, look at the lower left section of the 2019 SSA-1099, and expect to see a breakout of benefits for 2018 and benefits for 2019.  After entering the Box 5 number into TurboTax, along with any numbers for withholding and Medicare premiums, then expect to hit a Continue button (assumes next year same as this year) and you will get a prompt asking if there are any lump-sum payments for prior years.  You should answer yes if there are 2018 benefits on the 2019 form.  Then follow the instructions.  Next year, you should plan to have your 2018 tax return handy because you will likely need to enter values from the 2018 return to get the 2018 income taxed at a proper tax rate.