The correct answer is D. She told Dhiru that she was planning to leave the next day.
The sentence “She said to Dhiru, ‘I am planning to leave tomorrow'” is in the simple present tense. This means that the speaker is talking about something that is happening or will happen in the near future. In this case, the speaker is telling Dhiru that she is planning to leave the next day.
Option A is incorrect because it uses the past tense. The speaker is not talking about something that has already happened, but about something that is going to happen in the future.
Option B is incorrect because it uses the present continuous tense. The speaker is not talking about something that is happening right now, but about something that is going to happen in the future.
Option C is incorrect because it uses the modal verb “advise”. The speaker is not giving Dhiru advice, but simply telling him what she is planning to do.