elder brother's wife
嫂 refers specifically to an elder brother's wife, a familial relationship term.
嫂 combines 女 (woman) with 叟, which likely contributes the sound and may relate to an older meaning of 'old man', suggesting a mature woman in the family.
A woman (女) beside 叟, which looks like an old man with a cane, represents the elder brother's wife who cares for the family.
For ソウ, imagine the elder brother's wife sewing (ソウ) clothes for the family: sew -> ソウ.