Flo was a journalist who had worked all over the world, and was the aunt of Mary Richards. It was her liberal aunt that helped spark Mary to become a journalist herself.
She made infrequent visits to Minneapolis to make sure her niece was all right. She also battled Mary's boss, Lou Grant periodically, because she was flaming liberal, and he was somewhat conservative. Although, they clashed, there was a spark between the two of them. The two eventually had a quick fling.
After Lou moved to Los Angeles to work at the LA Tribune, Flo made a visit to him, to keep him updated on how Mary was. For despite their differences, they still cared about Mary. (Flo was, in fact, the only character from the Mary Tyler Moore Show to appear on Lou Grant, other than Lou, himself.)