Since she is over 65, she will need to file a tax return if her gross income is over $13,600. Gross income means all income she receives in the form of money, goods, property, and services that isn't exempt from tax, including any income from sources outside the United States or from the sale of her main home (when that happens). Don't include any social security benefits unless one-half of her social security benefits plus her other gross income and any tax-exempt interest is more than $25,000 (for Single Filers). Unfortunately, I can't do the calculations for you, but you can read more about the filing requirement here Tax Guide For Seniors. Hope that helps!
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