A striking girl even at the tender age of seven, Sofia Vassilieva began her career in show business as a child model. Within a few years, she was appearing on an episode of the CBS series The Agency, and in the made-for-TV movie The Brady Bunch in the White House. Vassilieva then took on the role of beloved children's book heroine Eloise for two TV movies about the character. Then in 2005, the then 13 year old was cast as Ariel, the daughter of Patricia Arquette's character on the supernatural drama Medium. She would stick with the series for several seasons, but also took on other projects, like the role of a girl suffering from leukemia in the 2009 drama My Sister's Keeper.