Complex sentence: During the Titanomachy, she betrayed the Olympian gods and joined the Titans against them; she became the messenger for the Titans, while her sister Iris was on the opposite side and became the messenger of the Olympian Gods.
Split into simpler sentences: During the Titanomachy, she betrayed the Olympian gods and joined the Titans against them; she became the messenger for the Titans. While her sister Iris was on the opposite side and she became the messenger of the Olympian Gods.