You can claim your mother as a dependent if she has less than $4400 of taxable income AND you paid more than half her total support. Remember that even though social security is not taxable if it is her only income, it still counts as support she provides herself, so you have to count that against the value of support you provide.
If you claim your mother as a dependent, you can also deduct medical expenses you paid for her, if you itemize your deductions.
If your mother has more than $4400 of taxable income, but you still provide more than half her total support, you can also deduct her medical expenses that you pay, even though you can't claim her as a dependent.
