You do not report a dependent's SS on your tax return.
If your sister receives Social Security survivors/disability benefits, that is income to her, not to you. You do not enter it on your tax return. Look at Box 2 of the SSA-1099 and you should see your sister's SSN.
If that is the only income your sister has, then she does not have to file or report it either.
If she has enough other income to be required to file, then she reports the SS on her own return.