Pointing to a lady in a picture, Saumya said, “She is the sister of the father…

Blood-relation puzzles are solved by substituting every nested phrase with the exact person it names, working outward from the relation closest to the speaker one link at a time, while tracking each person's generation and gender — the final family term (brother, aunt, grandmother, and so on) falls directly out of that generation-and-gender combination.

1. “Mother’s son” is Saumya’s brother — a sibling who shares both parents with her.

2. Saumya’s brother’s father is simply Saumya’s own father, since siblings share the same father.

3. Saumya’s father’s sister is Saumya’s aunt — one generation above Saumya, on the father’s side.

Cross-checking: the statement nests exactly three relations — “sister of the father of my mother’s son” — and the chain above resolves each one in turn without skipping a generation, ending one level above Saumya with a female relative on the father’s side, which is precisely the definition of an aunt.

• Sister — would require the lady to be in Saumya’s own generation; here she is one generation above, as the father’s sibling, so “sister” does not match.

• Grandmother — would require the chain to move up two generations from Saumya (a parent of one of Saumya’s own parents); the statement’s wording supports only one generation above Saumya.

• None of these — the resolved relation, aunt, is already one of the listed options, so this catch-all does not apply.

So, the lady in the picture is Saumya’s aunt.