Gerta Liederhosen, often referred to as Mrs. Liederhosen, is Dieter Liederhosen's mother and a minor character in Pepper Ann.
Gerta moved to Hazelnut from Germany sometime around 1990 with Dieter, as part of an "obstetrician exchange program", as we learn in "The Way They Were".
She actually delivered Moose after Lydia's doctor was transferred to Germany to take Gerta's place.
It's unknown if she's still an obstetrician, as in "Hazelnut's Finest" it's mentioned that her emergency room skills saved someone's life.
She has a husband in Germany, as we learn in "To Germany with Love", when Dieter sends him a videotape about his life in Hazelnut, and it's mentioned in the same episode that Mr. Liederhosen's job keeps him in Germany.