Correct Answer: She said that Ruhi had slipped when she was trying to board the bus.

Solution : The first option is correct.

Indirect speech, also known as reported speech or indirect discourse, is a way of reporting what someone else has said without quoting their exact words.
Narration conversion:

• The reporting verb "said" changes into "said that".
• The simple past tense "slipped" changes to the past perfect tense "had slipped".
• Said will not get replaced with told, as there is no object in the sentence.

Therefore, the indirect form would be: She said that Ruhi had slipped when she was trying to board the bus.