Even though she is crippled from pollio, she is not crippled by feelings of inferiority.
In fact, she is talented and excels in many ways.
Having a handicapped body doesn't mean having an impaired personality.
Fanny understands that she can't help her parents on the farm, and she doesn't want to be a burden to them.
So she is determined to live an active and independent life.
She is such a responsible and diligent girl that she makes me feel as if I were still a child.