After volunteering to help organize a concert at the Charles Krug Winery, she was hired by the winery and became the first female tour guide in the Napa Valley. Although the Krug Winery was owned by the Mondavi family, she did not meet her future husband Robert Mondavi until after he broke away from the family and started his own winery in 1966. Biever joined the Mondavi Winery the following year, when she was hired as director of public relations. Mondavi and Biever had a long-time affair and eventually divorced their first spouses in the late 1970s. Robert Mondavi and Margrit were married in Palm Springs in 1980.