Marilou Danley had earlier returned to the US, where she was met by investigators looking for clues as to why he carried out his deadly shooting spree.
FBI agents were at Los Angeles airport to escort Ms Danley, who was in the Philippines at the time of Sunday night’s mass shooting – the worst in modern US history.
Footage reportedly showed the 62-year-old woman being taken in a wheelchair at LAX while flanked by uniformed police officers.
Clark County Sheriff Joe Lombardo, who has called her a “person of interest” in the attack, has said detectives “anticipate some information” from Ms Danley shortly.
He added that he was “absolutely” confident that authorities will find out what motivated Paddock to kill 59 people and injure more than 500 others at a country music festival.
Ms Danley, who has not been arrested, lived with the 64-year-old at his retirement community home in Mesquite, Nevada – and officials searching the property have found a number of weapons.
She was born in the Philippines, and is an Australian citizen.
According to Ms Danley’s brother Reynaldo Bustos, she has assured her family she has a “clean conscience” following the rampage that lasted 11 minutes.
Mr Bustos said he immediately contacted his younger sister when he saw the news that Paddock had opened fire on music fans from the 32nd floor of the Mandalay Bay Resort and Casino.
Speaking from the Philippines, Mr Bustos told ABC News: “I called her up immediately and she said, ‘Relax, we shouldn’t worry about it. I’ll fix it. Do not panic. I have a clean conscience’.”
Meanwhile, Ms Danley’s sisters have said they believe she was “sent away” so she could not interfere with her boyfriend’s plan to open fire on thousands of people in the massacre.
One said: “I know that she doesn’t know anything as well like us. She was sent away. She was away so that she will not be there to interfere with what he’s planning.”
Speaking to Seven News in Australia, the women said they were in complete shock to discover their sister had arrived in the Philippines two weeks ago.
One of them said Ms Danley was “a good person” who would have stopped Paddock if she had been there.
They also claimed Ms Danley had been sent $127,000 (£95,000).
This could be the same $100,000 which a US official said Paddock transferred to the Philippines in the days before the shooting.
Paddock, who had no previous record of violence or crime, was prescribed an anti-anxiety drug in June that can lead to aggressive behaviour, the Las Vegas Review-Journal reported.
It said records showed Paddock was prescribed 50 diazepam tablets by a doctor on 21 June.
Paddock bought the drug – also known as Valium – on the same day it was prescribed. He was supposed to take one pill a day.
Diazepam is a sedative-hypnotic drug in the class of drugs known as benzodizepines, which studies have shown can trigger aggressive behaviour.
Paddock sprayed a crowd below with hundreds of rounds. He took his own life before police broke into his hotel room, where they found 23 guns and 12 “bump stock” devices that can enable a rifle to fire continuously, like an automatic weapon.
President Trump has flown to Las Vegas, where he met some of the survivors of the attack and members of the emergency services.