Who is Isabelle Lightwood?
Isabelle "Izzy" Sophia Lightwood is a Shadowhunter and lives in the New York Institute. She was born in May 31, is the younger sister of Alec and Jace and is older than Max. Passionate and with a high sense of fashion. She is rebellious and very beautiful. Her cooking is often made fun of by Jace and Alec. She is known to be dangerous and often carries weapons in her tall boots that are never less than seven inches.

Isabelle is very beautiful and tall. She has very dark brown eyes with hints of gold that initially appear to be black. She is curvaceous and has long black hair that is described as "black as spilt ink" by Clary. She dresses stylishly, often with high heels. However, she despised her height and hated towering over everyone and wished to be small and delicate like Clary.

She is portrayed by Jemima West in the film adaptation of the book, and Emeraude Toubia in the television series.

Details and Trivia
Isabelle is the middle child in the Lightwood family. Her parents are Maryse and Robert Lightwood, who were once in the Circle with Valentine until the Uprising. Her older brother is Alec and her younger brother was Max, who died at the hand of Jonathan Christopher Morgenstern. Jace is her adoptive brother. Her parents run the Institute in New York.

Isabelle obviously cares for Jace and Alec, and is fiercely protective of both of them. Because of this, she is constantly torn over the fact that her brother is struggling with his sexuality and when Jace is heartbroken over Clary during their supposedly sibling relationship.

The ruby necklace that Isabelle wears throughout the show was originally not going to be used however, when fans began to argue its importance it was added into the storyline.

-- More About Izzy Wiki Link
-- IMDB Link
-- Wiki Fandom Link