From Wikipedia, the free encyclopedia. Sofia Vladimirovna Vassilieva (born October 22, 1992) is an American actress. She is best known for playing the children's book heroine Eloise, in two made-for-television movies, Ariel Dubois in the Emmy-winning TV series Medium, and the cancer patient Kate Fitzgerald in the 2009 film adaption of My Sister's Keeper by Jodi Picoult. Description above from the Wikipedia article Sofia Vassilieva, licensed under CC-BY-SA,full list of contributors on Wikipedia.