We cannot see your tax return or your screen and you have provided no other information about your income.  

Her SS may or may not be taxable.

Up to 85% of Social Security becomes taxable when all your other income plus 1/2 your social security, reaches:

Married Filing Jointly: $32,000

Single or head of household: $25,000

Married Filing Separately: 0

She can have withholding taken out of her SS.