The correct option is
C She said that she was an early-riser.
The given sentence is a statement.
According to the rules of narration and reporting, if the reporting verb is in the past tense, the tense of the reported verb is changed into its corresponding past form. The reporting verb in the given sentence, 'said', is in the past form. Therefore, the reported verb, 'am' will change into 'was'. The first person pronoun 'I' will change to third person 'she'
Thus, in indirect speech the sentence must be,
She said that she was an early-riser.
Thus option C is the correct answer.
Options A,B,D are incorrect as they do not follow the rules of Narration and Reporting.