First, to claim your mother as a dependent, she can't have more than $4300 of taxable income. Social security is not taxable if it is her only income. You must also pay more than half her total living expenses. Although her SS benefit does not count as taxable income, it does count as support she provides herself, so you have to determine if--after including her SS benefit--do you pay more than half her total support.
Then, to deduct your mother's medical expenses that you pay for, you must either be able to claim her as a dependent, or be disqualified from claiming her as a dependent only because of her taxable income or marital status. In other words, if you provide more than half her total financial support, you can deduct medical expenses you pay even if you can't claim her as a tax dependent.
