Dziena was born in New York City of Irish, Italian, and Polish descent. She attended Saint Ann's School alongside her Bringing Rain (2003) costar, Paz de la Huerta. She spent many of her summers growing up in the small South Jersey shore town of Sea Isle City. Also, during high school, she attended classes at the American Academy of Dramatic Arts and appeared in plays there as well.

Dziena made her acting debut in TNT's Witchblade.

One of her first major roles was in the Lifetime Channel original She's Too Young, in which she portrayed a sexually active teenager alongside Miriam McDonald of Degrassi: The Next Generation fame.

She appeared as a character called Lolita in Broken Flowers, which includes a scene in which she appears fully nude. She also played the role of Heather, a sexually frustrated young woman in a loving relationship, who takes part in a couple swap as part of therapy in the film Sex and Breakfast. The film also starred Eliza Dushku and Macaulay Culkin. In the ABC television series Invasion she played the sheriff's daughter Kira Underlay. Dziena also appeared on the sixth season of the HBO series Entourage.

In addition to acting, Dziena is a budding playwright and drummer.