Who is Ada Black from Extremely Loud and Incredibly Close and what is their importance?

Oskar Schell's interviewee in Manhattan who owns two Picasso paintings, but knows nothing about the key. They debate the ethics of wealth. Oskar wonders how Ada knows his name, not recalling having given told her it. She allows him to snoop around the apartment and decides she likes him, wishes him luck, and sends him home in a cab.