Explanation:

- Roshni met a man in the market who is described as the only son of her mother's father's wife.

- "Mother's father's wife" translates simply to Roshni's grandmother, assuming no step-relations are involved.

- The only son of Roshni's grandmother would be Roshni's mother's brother, making him Roshni's maternal uncle.

- Therefore, this man is Roshni's uncle, and R's wife would be Roshni's aunt.

- Option 1 (Sister) is incorrect as a sister is not married to an uncle.

- Option 3 (Mother) is incorrect, she is related more directly as her daughter’s mother.

- Option 4 (Daughter) is incorrect as she cannot be daughter's aunt.

So, Option 2 (Aunt) is correct.

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