Social security (SS) only becomes taxable when added to sufficient other income. If you are otherwise required to file a tax return, you do need to enter it in Turbotax (TT). TT will determine the taxable portion.
There is a special rule that says SS becomes taxable at zero ($0) other income when Filing as Married Filing Separately (MFS). The calculation is a little complicated. But, a simple answer is: she does not need to file is she has less than $12,000 income, including SS.
You may be thinking that filing MFS is going to save you money, because you don't have to add her income to your return. That thinking is wrong. The doubled standard deduction will wipe out all her income, on a joint return. But you will still get the use the lower joint filing rates.
Before making a decision to file as MFS, you should run test returns and compare. You can use this tool:
https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1
