Nidhi, who is not an accused in the case, was examined about details relating to alleged conspiracy to eliminate Dabholkar as the agency believes she might be witness to some development when it was being hatched, sources said.
Searches were also carried out at her properties on the outskirts of Mumbai.
Sources said the agency has information about her participation in programmes against Dabholkar with her husband, besides, she had been an active member of Sanatan Sanstha, which is under scanner in the case.
Dabholkar was shot dead by two unidentified men during morning walk on Omkareshwar Bridge in Pune on August 20, 2013.
More From This Section
Tawde and Akolkar wanted to eliminate Dabholkar in 2009 itself, but they dropped the plan due to the Margao bomb blast which took place the same year, CBI sources said, citing evidence pieced together by the agency.
Tawde, suspected to be the mastermind of the conspiracy, kept on planning a hit on the activist along with Akolkar. The plan was finally executed on August 20, 2013, they said.
The sources also said Tawde hated Dabholkar for his relentless campaign against superstition. He also allegedly played a key role in the 2009 Sangli-Miraj riots.
The Sanstha has denied any role in Dabholkar's murder and termed Tawde's arrest as "mysterious".