In this chain relation problem, we are asked: "How is Radha's mother's mother's daughter in law's daughter related to Radha?" The question involves several generations and in laws in Radha's family.

Introduction / Context:
This question presents a long descriptive chain: Radha's mother's mother's daughter in law's daughter. It is a typical exam style blood relation puzzle where we must carefully move step by step through generations. The goal is to determine the relationship of the final person, the daughter, with Radha. Such questions reward methodical tracking more than speed.

Given Data / Assumptions:
• Start from Radha and move upward to her mother.• Radha's mother's mother is Radha's maternal grandmother.• The daughter in law of Radha's maternal grandmother is the wife of the grandmother's son.• That son is Radha's maternal uncle.• The daughter in law's daughter is the child of this maternal uncle and his wife.• Standard assumptions about terminology are used.

Concept / Approach:
By breaking the chain phrase into simple steps, we see that we are essentially talking about the daughter of Radha's maternal uncle and his wife. A child of one's maternal uncle is a cousin, specifically a maternal cousin. Thus the final girl in the chain is not a sister or niece of Radha, but her cousin. The critical part is correctly interpreting daughter in law of the grandmother as the wife of the grandmother's son, not as the spouse of any grandchild.

Step-by-Step Solution:
Step 1: Radha's mother's mother is Radha's maternal grandmother.Step 2: The daughter in law of Radha's maternal grandmother is the wife of the grandmother's son.Step 3: The grandmother's son is Radha's maternal uncle.Step 4: Therefore the daughter in law is Radha's maternal aunt by marriage.Step 5: The daughter referred to in the chain is the daughter of this maternal uncle and aunt.Step 6: A daughter of one's maternal uncle is one's cousin, specifically a maternal cousin.

Verification / Alternative Check:
Draw a simple tree: at the top is Radha's maternal grandmother. She has at least two children, Radha's mother and Radha's maternal uncle. The maternal uncle has a wife (the daughter in law of the grandmother) and a daughter. Radha is a child of the grandmother's daughter, while the final girl is a child of the grandmother's son. Children of a brother and a sister in the middle generation are first cousins. Hence the relationship is cousin.

Why Other Options Are Wrong:
Sister in law of Radha: A sister in law would be the wife of Radha's brother or the sister of Radha's spouse, which is not implied here.Sister of Radha: For her to be a sister, they would share the same parents, but the chain clearly leads through the maternal uncle, not Radha's own parents.Aunt of Radha: An aunt would be a sister of a parent or the wife of an uncle, not the daughter of an uncle.Niece of Radha: A niece would be the daughter of Radha's sibling or sibling in law; that is a lower generation, not the same generation as Radha.

Common Pitfalls:
Students often misplace the daughter in law in the wrong generation or think of her as the wife of Radha's father rather than the wife of the grandmother's son. Another frequent mistake is to assume that any daughter in such a chain is automatically a niece or a sister, without checking which parent she belongs to. Carefully tracing each step avoids these confusions.

Final Answer:
The daughter in the chain is the cousin of Radha.