In decipher jumbled up description type of questions, a round-about description is given in the form of certain small relationships and direct relationship between the persons concerned is to be deciphered.
A man pointing to a photograph says, "The lady in the photograph is my nephew's maternal grandmother."
How is the lady in the photograph related to the man's sister who has no other sister ?
Clearly, the lady is the grandmother of man's sister's son i.e., the mother of the mother of man's sister's son i.e. the mother of man's sister.
So, the lady is man's mother.