Pointing to a lady in the photograph, Nisha said, ‘Her son’s father is the…

In blood-relation puzzles, a phrase such as ‘the only son-in-law of my mother’ or ‘the only child of her parents’ fixes ONE specific family member as the sole holder of that role. Converting each relational phrase (son’s father, son-in-law, only child) into an actual person, one link at a time, is how these self-referential puzzles are solved — when two different phrasings resolve to the SAME person, the puzzle is describing someone’s relation to themselves.

1. ‘Her son’s father’ refers to the husband of the lady in the photograph, since a son’s father is always his mother’s husband.

2. ‘The only son-in-law of my mother’ refers to the husband of one of Nisha’s mother’s daughters.

3. Nisha is the only child of her parents, so Nisha’s mother has exactly one daughter — Nisha herself; the mother’s only possible son-in-law is therefore Nisha’s own husband.

4. Equating the two descriptions of the same person (the lady’s husband, from step 1, and Nisha’s mother’s only son-in-law, from step 3): the lady’s husband and Nisha’s husband are the same person, so the lady and Nisha are the same person.

Since the lady in the photograph is Nisha herself, none of the listed relations (Sister, Sister-in-law, Niece) — which all describe a relation to someone else — can apply; a person’s relation to herself is not among them, so the answer is ‘None of these’.