Who is Astrid Menks from Buffett: The Making of an American Capitalist and what is their importance?

Astrid was a waitress at the French Cafe where Susie Buffett had singing engagements. She was raised primarily in an orphanage and lived in the bohemian section of Omaha, leading a very different life from the Buffetts. When Susie left Warren, she encouraged Astrid to drop in on Warren and fix him a few meals. Within a year, Astrid had moved into the Buffett home with Susie's blessing. Together they have remained, and move about Omaha as any typically married couple. Warren, however, is still married to Susie whom he sees at least once a month.