Cecily Herondale
Wikipedia
A Guide to The Infernal Devices
Cecily Herondale is Will Herondale's younger sister whom he left alongside their parents after he believed that he accidentally caused their older sister, Ella's death when he was 12 years old. Later, Will learned that he was not the cause of Ella's death.
Even after many years have passed, Will still remembers and misses Cecily. In turn, Cecily also misses her brother terribly and is relieved when Ragnor Fell does not deny that he visits the Herondale residence on Will's behalf.
Eventually, Cecily becomes a Shadowhunter, at first to convince Will to return home, but Later because she realizes that the world which she taught was dangerous is actually challenging and enjoyable. At the end of Clockwork Princess, Cecily marries Gabriel Lightwood and they have three children together, Anna, Christopher, and Alexander Lightwood.
Even after many years have passed, Will still remembers and misses Cecily. In turn, Cecily also misses her brother terribly and is relieved when Ragnor Fell does not deny that he visits the Herondale residence on Will's behalf.
Eventually, Cecily becomes a Shadowhunter, at first to convince Will to return home, but Later because she realizes that the world which she taught was dangerous is actually challenging and enjoyable. At the end of Clockwork Princess, Cecily marries Gabriel Lightwood and they have three children together, Anna, Christopher, and Alexander Lightwood.