Personality wise, Lucie and Clary are eeriely similiar yet different. It easy to tell them apart as Lucie, even though moments younger, is more head strong, protective and stubborn than her sister, often causing more clashing with their mother. She is also the first one to be sarcastic and more so than Clary, despite this she is slightly more confident, compassionate, empathic and loving to those around her. She is extremely determined and won't stop until she has achieved what she wants.
Valentine states that he is happy to see that even though the girls look like their mother, at least one of them is like him. With her charismatic and genius level intellect, he accepted her rather than hate her like Clary. But with her empathy and compassion, which he vowed to drive out of her, she refused to abandon her sister, mother and her true father, Luke.
Lucie was insecure that everyone called her Clary before they said her name, which Clary tells her it is the same for her. They would say 'Lucie' before Clary, which eases Lucie's insecurities about her sister.
Like Clary, Lucie has an artist side but instead of drawing like her sister, Lucie tends to write her emotions and feelings into her stories and diary. Unless it comes to the ruins when she doodles everywhere and in everything she does.
Like her twin, Lucie looks exactly like a younger version of her mother. More confident in her appearance, Lucie appreciates her freckles, green eyes and red curls. Her smaller stature makes her feel as if the world looks down on her sometimes.
While she dresses in more girlier outfits than her sister, often unknowningly, Lucie will wear the exact outfit Clary wears if they don't catch each other before going somewhere. Though she hates wearing the outfits that Isabelle picks out, Lucie will often try to change them in some way. But unlike her sister, Lucie's tastes never change.