Official sources said the IO recorded her statement here under the provisions of the Prevention of Money Laundering Act (PMLA) during the questioning which lasted over four hours.
They said she was also confronted with the statements made by other accused in the case, including LIC agent Anand Chauhan, who was arrested by the agency last month.
The agency had earlier issued summons to her to appear before the Investigating Officer (IO) today.
ED had yesterday told the HC that it has no intention as of now to arrest Pratibha.
Sources had earlier said the questioning of the CM's wife was "essential" to thoroughly probe the case after some "revelations" were claimed to have been made by Chauhan.
The agency had attached assets worth about Rs eight crore of the Chief Minister earlier this year. Singh has denied allegations of any wrongdoing by him and his family.
It had also conducted searches in this case last year in Delhi, Maharashtra and West Bengal.
The agency is probing allegations against Singh and his family members of having amassed wealth of Rs 6.1 crore disproportionate to his known sources of income between 2009 and 2011 when he was the Union Minister of Steel.
The CBI's First Information Report had named Singh, Pratibha, Chauhan and his brother C L Chauhan, who were all accused of violating the provisions of the Prevention of Corruption Act.
