The sentence in the Direct Speech is in Present Perfect Tense. Therefore, the sentence in the Indirect Speech should be in Past Perfect Tense.
Present Perfect (Subject + has/have + V3 +Object) should be converted into Past Perfect (Subject + had + V3 +Object).
For example:
He said, "I have got a new job." (Direct Speech)
He said that he had got a new job. (Indirect Speech)
The following things in the sentence should change when changed from Direct speech to Indirect Speech:
'This week' would be changed to 'that week'.
'Has spoiled' would be changed to 'had spoiled'.
'My' would be changed to 'her'.
Since there is no object of the verb 'said' in the sentence in direct speech, 'said' would be changed to 'said that' only.
Therefore, the correct answer is option (a): Shikha said that the heavy rain that week had spoiled all her travel plans.