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Father’s sister: Aunt; Aunt’s daughter: Cousin Sister. So, the daughter of the only sister of father: Cousin Sister. 

The correct option is D. Cousin Sister. A cousin is a relative with whom a person shares one or more common ancestors. In this statement, the lady is the daughter of the only sister of Simon's father, so the lady is Simon's cousin sister.

Definition of Cousin: A cousin is a relative with whom a person shares one or more common ancestors.

In the given statement, Simon is pointing to a lady and saying that she is the daughter of the only sister of his father. It means that the lady is not a sibling of Simon's father, but is a relative of his father. Therefore, the lady is Simon's cousin sister.

The relationship between Simon and the lady can be shown in the following family tree:

Simon's Grandfather
|
Simon's Father
|
Simon (given)
|
Lady (mentioned)

Thus, it is clear that the lady is Simon's cousin sister.

To summarize, the correct option is D. Cousin Sister.