Explanation:

- Deepika points to a girl, referring to her as "my mother-in-law's only son's niece."

- Deepika's mother-in-law's only son would be Deepika's husband.

- The girl's uncle is Deepika's husband, making the girl the daughter of Deepika's sibling or sibling-in-law.

- Therefore, the girl's mother is either Deepika's sister or sister-in-law.

Upon evaluating the options:

- Sister (Option 1): Would mean the girl's uncle through her mother is Deepika's sibling, but the key relationship mentioned involves the husband (brother-in-law) rather than a direct sibling.

- Sister-in-law (Option 2): Matches as the girl's mother is Deepika's husband's sister.

- Daughter-in-law (Option 3) and Cousin (Option 4) are not relevant in this scenario.

Answer Option:2 Sister-in-law is the correct choice. .