Pointing to a woman in a photograph, Ram says, "She is the only daugh…

Let's break the statement down:

"She is the only daughter of the mother-in-law of my only son."

1. My only son → Ram's son.
2. My only son's mother-in-law → The mother of Ram's son's wife.
3. The only daughter of that mother-in-law → Ram's son's wife.

Therefore, the woman in the photograph is Ram's daughter-in-law.