Looking at a photo of a person a girl said, "His daughter's paternal uncle's wife is my mother." What is the relation of that girl to the mother of the person in the photo?

"His" → (Refers to the person in the photo.)
"His daughter’s paternal uncle" → (The paternal uncle of his daughter is his own brother.)
"His daughter's paternal uncle's wife" → (His brother's wife.)
"His daughter's paternal uncle's wife is my mother." → (The girl’s mother is the brother's wife, meaning she is the daughter of the person's brother.)

According to the given information, the family tree diagram will be:

The girl's father is the brother of the person in the photo.
The mother of the person in the photo is also the mother of his brother.

The girl is person's mother granddaughter.
Thus, the correct option is (a) Son's Daughter.