Step 1 — Read the original sentence:
Direct speech: She said to him, “Why don’t you go today?”
Step 2 — Identify the reporting verb:
The sentence is a question, so in indirect speech the reporting verb "said to" changes to "asked".
Step 3 — Convert the question form:
The direct form is "Why don’t you go." In indirect speech, this changes to "why he did not go."
Step 4 — Change the time expression:
"today" becomes "that day" in indirect speech.
Step 5 — Construct the indirect speech sentence:
She asked him why he did not go that day.
Final Answer:
The correct option is (D) : She asked him why he did not go that day.