Om Lydia Branwell
"Lydia Branwell is a character who was invented for the show. I didn’t know much about her beyond her involvement with Alec (Maryse wants to marry Alec to her), so I asked Ed, and he said Lydia was created because “we had to sort of bring Idris to the Institute! We need that larger story you have in the novels about the Accords and the role that the original families play in the history of the Shadowhunters, so we had to bring someone to the Institute to embody that.“ He also said she is an obstacle to Magnus and Alec’s romance about which they are enthusiastic. One of the other writers, Angel Dean Lopez, said the girl Alec was going to be involved with (Lydia) was “a lot like him in personality.” I know she says in her audition that she was in love with “John Blackthorn” (but don’t know if he ever shows up as a character.)
There’s a big story on The Wrap about the casting and the actress, Stephanie Bennett.