Complex sentence: Additionally, she played the nasty Aunt Marge in "Harry Potter and the Prisoner of Azkaban", and Miriam, a motherly activist in "Children of Men", both of which were directed by Alfonso Cuarón.
Split into simpler sentences: Additionally, she played the callous Aunt Marge in "Harry Potter and the Prisoner of Azkaban". Following her roles as those two unpleasant characters, Ferris took on the role of Miriam, a motherly activist in "Children of Men"; that film and the one before were both directed by Alfonso Cuarón.