The original sentence is in Direct Speech with the present perfect tense: “I have completed…”.
When converting to Indirect Speech, the tense usually shifts one step back:
- Present Perfect (have completed) \(⇒\) Past Perfect (had completed).
Also, the pronoun “I” changes to “she” (since the speaker is “she”).
Thus, the correct transformation is:
\(⇒\) “She said that she had completed her assignment on time.”