I have received a Statement of Survivor Annuity Paid CSF1099R from the Office of Personnel Management. The taxable amount and Total Emp Contr. States Unknown. HELP

I'm completing my mother in Laws tax return who is 88. Her husband would have been 91 this year and she has been receiving this annuity since his passing 15 years ago. I don't know what to plug into the TurboTax fields. When researching this they talk about Simplified and General rule calculations vis Publication 721which is a 100 page long. HELP