Blood relations – identity of self vs sibling: Pointing to a girl, Nidhi said, "She is the only daughter of my grandmother's only child." How is the girl related to Nidhi?

Introduction / Context:
This tests recognition that "grandmother's only child" must be Nidhi's parent, and "only daughter" of that parent uniquely identifies Nidhi herself if she is female.

Given Data / Assumptions:

• Grandmother has exactly one child ⇒ Nidhi's parent.
• The referenced girl is the only daughter of that parent.
• Nidhi is female (typical name-based assumption used in such puzzles).

Concept / Approach:
If a parent has only one daughter and Nidhi is a daughter of that parent, then Nidhi herself is that "only daughter." Therefore the girl being pointed at is Nidhi (i.e., the relation is "Self").

Step-by-Step Solution:

Verification / Alternative check:
If there were any other daughter, "only daughter" would be contradicted. If Nidhi were not the daughter, she would not call the person "my grand­mother's only child" her parent.

Why Other Options Are Wrong:
Sister/Cousin/Aunt introduce extra daughters or other branches, violating "only daughter."

Common Pitfalls:
Overlooking the exclusivity implied by "only."

Final Answer:
Self