The court is not concerned how you got the documents, as long as it is true.
However, the girl might file a case for hacking and other things seperately.
You won't get income tax returns in RTI, you would have to call the Income Tax Returns through CrPC 91 application or Witness Summons as the case may be.
Regards,
Shonee Kapoor
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If you don't fight for what you want, don't cry for what you LOST.