SS benefits are not taxable unless you also have too much other income. If the only other income your friend had other than SS was $2,000, then she would not owe taxes and is not required to file a return.
The rent credit is a state credit she may be eligible for, but even this credit only applies if you owe taxes to begin with. Since she owes no taxes and is not even required to file a return, the rent credit would not even apply.
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Thank you Jarod