Complex sentence: The church was commissioned by Margherita Gonzaga, the widow of Alfonso II d'Este, who, while not a nun herself, came to live in an apartment in the Clarissan monastery that was once adjacent (destroyed in 1930).
Split into simpler sentences: The church was commissioned by Margherita Gonzaga d'Este, the widow of Alfonso II d'Este. Margherita, while not a nun herself, as a widow came to live in an apartment in the Clarissan monastery that was once adjacent (destroyed in 1930).