Hrmm.. Android in appearence with a neutrual or blank expression most of the time. Pale skin, light colored hair, like brown or red. Early thirties. Maybe about 5'8. A frail frame, not from malnurshiment mind you. I imagine Siri would have short hair, maybe shoulder length. Considering that she's never been asked her opinion, or her thoughts, she would be indecisive, or one who would go along with what someone else wants, or someone who would follow others.