Faiza Outalha is said to have made a reconnaissance trip to the state in 2008.
The NIA officials believe she also visited the Kalyani helipad and The Retreat, the summer holiday resort of the Indian president, on the outskirts of Shimla.
"The investigators have scrutinised and collected log books of the resort and recorded the statements of their staff members. They also visited The Retreat and examined the visitor's book there," the police official said.
"Headley himself had never visited Manali but we understand that Outalha did. We are still in the process of collecting evidence," said another intelligence official in New Delhi.
"So far the investigators have not been able to lay hand on any concrete evidence, suggesting Outalha's visit to towns in Himachal Pradesh," the official added.