No, Social Security does not have any relationship to the individual's filing status.
If she doesn't have any additional income other than Social Security she will not have to file a tax return. Provided she lives with you and does not provide more than 1/2 of her living expenses, it would be wise to claim her as a dependent.
We dont file a tax return for her.
But how does me covering the cost of her living expense affect her SSI? Does she have to pay a fair share so that way its not reduced??