Complex sentence: Pumpkin was looking forward to the adoption so that she could have some kind of security in her old age, while Hatsumomo was looking forward to Pumpkin's adoption just so she could secure her own position as head geisha and drive Sayuri out of Gion.
Split into simpler sentences: Pumpkin was looking forward to the adoption so that she could have some kind of security in her old age. While Hatsumomo was looking forward to Pumpkin's adoption just so she can secure her own position as head geisha and drive Sayuri out of Gion.