Police will interview Marilou Danley, on Wednesday after a law enforcement official confirmed that the 64-year-old shooter wired the sum her ahead of his killing spree.
Sheriff Joe Lombardo said police expected more information from her "shortly".
One friend, Betty Dixon, who attended dance and exercise classes with Danley, described her as a wonderful woman.
Paddock wired $100,000 to an account in Danley's home country, the Philippines, in the week before he unleashed the worst mass shooting in modern USA history, according to multiple senior law enforcement officials.
Danley and Paddock reportedly lived together in the suburbs in Mesquite, Nevada. A neighbor, Susan Page, told the newspaper that Paddock and Danley were "closet people" and that she "never saw them".
United States expels 15 Cuban diplomats
They are believed to have been "targeted" either in their residences within compounds owned by the Cuban government, or in hotels. It also suspended issuing visas to Cubans, a step that makes it hard for Cuban Americans to reunite with relatives.
Much still remains unknown about the shooter, his motive and how much, if anything, his girlfriend knew about his plans to commit the horrific act.
This is a developing story. CNN reports the sisters are Australian residents who say their sibling was "really in love with Steve". "She was away so that she will be not there to interfere with what he's planning", one sister who lives in Queensland told Channel 7. "She probably was even shocked than us because she was more closer to him than us", one sister said.
The shooter, 64, killed at least 58 people and injured 527 others Sunday night in the deadliest mass shooting in modern US history. Twenty-two thousand people were in attendance; 59 were killed and another 527 wounded.
"The fact that he had the type of weaponry and the amount of weaponry in that [hotel] room - it was preplanned extensively", Lombardo said.
Pictures have emerged from the hotel room showing Paddock lying dead, surrounded by weapons and spent ammunition.