Preparing the family tree by using the following symbols
From the statements:
Swathi is the daughter of Anil.
Anil's mother is Gouri.
Kamini is Gouri's mother.
Kamini's husband is Gaurav. (This means, Gaurav is the father of Gauri)
Poonam is the mother-in-law of Gourav. (This means, Poonam is the mother of Kamini)
The table shows the relation among the members of the family:
Thus, Swati is the great-granddaughter of Gaurav.
Hence, Great granddaughter is correct.