The US source said Danley was not under arrest but that the Federal Bureau of Investigation hoped she would consent to be interviewed voluntarily.
"She was away so that she will be not there to interfere with what he's planning", one of Danley's sisters told 7 News from their home in Australia's Gold Coast region.
She had traveled to Hong Kong and Manila in the days before Paddock's attack.
"No one can put the puzzles together, no one, except Marilou, because Steve is not here to talk anymore".
"If Marilou was there, this maybe as well didn't happen because she won't let it happen".
"The reason Mary Lou looks so plain in that picture they keep posting of her is because for him she would not wear perfumes or hair sprays or anything with scents in it because it affected him", Eric Paddock wrote, referring to a passport-style photo of Danley that has been widely circulated by news outlets.
Clark County Sheriff Joseph Lombardo named the 62-year-old as a "person of interest" shortly after the mass shooting Sunday night.
Mangrobang added Danley had arrived in the Philippines from Tokyo on September 15. It can make the gun fire three or four times with each turn of the crank, significantly faster than using a finger to pull the trigger.
Paddock had transferred $100,000 to his girlfriend in the Philippines a day before the strike.
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Other reports have said she left the country on Sept 25.
Danley's social media sites showed she was a regular world traveller. Audio recordings from the scene strongly suggest that at least one of the guns was a fully automatic weapon or had been re-fashioned to operate like one.
Police said Paddock strafed the concert crowd with bullets for nine to 11 minutes before taking his own life, and had set up cameras inside and outside his hotel suite so he could see police as they closed in on his location.
But converting a semi-automatic weapon, including the AR-15 and AK-47-type assault rifles widely available in U.S. gun shops, into an automatic weapon is easy.
Danley was in the Philippines at the time of the shooting, according to law-enforcement officials.
She and Geary Danley reportedly divorced in 2015 and she was living with Paddock in Mesquite, Nevada, 130km from Las Vegas. It's unclear when the couple met. The devices are legal under USA law, even though fully automatic weapons are for the most part banned.
She was working as a hostess at the Atlantis Casino Resort Spa in Reno, Nevada's capital, when she met Paddock, a wealthy gambler, according to his brother.
Speaking to CNN affiliate KHBS, the daughters of Danley's ex-husband described their former stepmother as a "good and gentle person".
"I called her up immediately and she said, 'Relax, we shouldn't worry about it".
"This is a horrific event, and our hearts and prayers go out to everyone impacted by this bad act", Waltrip said. The investigation agency is ascertaining whether the woman had prior knowledge of Stephen Paddock's nefarious plan.