Complex sentence: Lysa Arryn is the second child and youngest daughter of Lord Hoster Tully who was in love with Petyr Baelish, hating her older sister Catelyn Tully as he fell in love with her.
Split into simpler sentences: Lysa Arryn is the second child and youngest daughter of Lord Hoster Tully. Enamoured of Petyr Baelish, Lysa resented her older sister Catelyn Tully when he fell in love with her.