The following article contains an answer for the question: How does the singer know Lise? , can you please find it? 

American World War II veteran Jerry Mulligan is an exuberant expatriate in Paris trying to make a reputation as a painter. His friend and neighbor, Adam Cook, is a struggling concert pianist and longtime associate of a French singer, Henri Baurel. At the ground-floor bar, Henri tells Adam about his cultured girlfriend, Lise Bouvier.  Jerry joins them later, before going out to sell his art.
A lonely society woman and heiress, Milo Roberts, finds Jerry displaying his paintings in Montmartre and takes an interest in him and his art.  She brings him to her apartment to pay for his works, and invites him to a dinner party she is throwing later that night. After singing with French children on the way home ("I Got Rhythm"), Jerry goes up to Milo's apartment.  He quickly finds out the "party" is actually a one-on-one date, and tells Milo he has no interest in being a paid escort.  When he attempts to leave after giving her money back, she insists she is only interested in his art.
They go to a crowded bar, and Milo offers to sponsor an art show for Jerry as a friendly gesture.  Some of Milo's friends arrive, and while sitting with them, Jerry sees Lise seated with friends at the next table, and is instantly smitten. He ignores Milo and her acquaintances, and instead pretends to know Lise already and dances with her.  She is standoffish and gives Jerry a wrong phone number, but is innocently corrected by someone at her table.  Milo is upset by Jerry's behaviour and suddenly decides to go home. On their way home she tells Jerry he was very rude cavorting with a girl he does not know while in her presence; tired of Milo, Jerry gets out of the car and bids her farewell.

his cultured girlfriend