Step 1: Understanding the Question:
This is a blood relation problem where a speaker (Ravi) describes his relationship to a woman by mentioning her mother's relation to his own mother.
Step 2: Detailed Explanation:
1. Let us break down the descriptive statement: "Her mother is the only daughter of my mother."
2. First, let us evaluate the phrase from the speaker's (Ravi's) perspective: "the only daughter of my mother".
- The only daughter of Ravi's mother is Ravi's sister.
3. Now, let us substitute this simplified relationship back into the original statement:
- The statement becomes: "Her [the woman's] mother is Ravi's sister."
4. Now, analyze the relationship between Ravi and the woman:
- The woman is the daughter of Ravi's sister.
5. By standard terminology in family relations:
- The daughter of one's sister or brother is defined as a niece.
- The son of one's sister or brother is defined as a nephew.
6. Therefore, the woman is Ravi's niece.
Step 3: Final Answer:
The woman is related to Ravi as his Niece. Hence, the correct option is (D).