Euphemia has been shown to have her humanity and emotions on, while her twin brother has them off. Even with the demon blood that was in her, she still show emotion, and Jocelyn had hoped for her daughter to there to be good in her.
Euphemia could also be viewed as the exact opposite of Jonathan, but be like her adoptive brother, Jace. She is not cold-hearted, cruel, sadistic and ruthlessness, but quite the opposite of that, and even showing some disgust and hatred and fear to Jonathan and Valentine.
Euphemia was taught to feign human emotion by her father, but the feign emotion was instead true emotions, having an deep concern, worried and love towards Jace, Clary and Jocelyn.
During the sibling abuse from Jonathan, Euphemia was shown to have disgust, hatred and fear towards him, even coming up with the courage to escape from Jonathan and Valentine and entering the mundane world.
When she entered the mundane world, she was curious and happy to be away from her family, having the relaxtion and peaceful demeanor, but always had the paranoid of her brother finding her.
Euphemia stands at 5'8", with an slim body, with long dark hair and brown eyes. She has faded runes on her body as well as scars from her abuse from Jonathan.