You have not mentioned her age. If she had more than $4300 of income NOT counting the Social Security you cannot claim her as a dependent. The SS is taxable only if she had enough other income to make it taxable. Did she work---even at a part-time job--and have more than $4300 of income from working? Or does she receive any other sort of income like a pension, rental income, etc.?
She might be your qualifying relative, for whom you can get the $500 credit for other dependents.
CREDIT FOR OTHER DEPENDENTS
https://ttlc.intuit.com/questions/4499708-what-is-the-500-credit-for-other-dependents-family-tax-cre...
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent
https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
