Complex sentence: Armitage began her professional career in 1973 as a member of the Ballet du Grand Théâtre de Genève, Switzerland, a company directed by George Balanchine and Patricia Neary that was rooted in the Balanchine aesthetic and devoted exclusively to his repertory.
Split into simpler sentences: Armitage began her professional career in 1973 as a member of the Ballet du Grand Théâtre de Genève in Switzerland. This was a company directed by George Balanchine and Patricia Neary which was rooted in the Balanchine aesthetic and devoted exclusively to his repertory.