She began acting professionally at 15 and appeared in two films, Mujeres en el Acto and Arresto Domiciliario in 2006 and 2008 both by the acclaimed Director, Gabriel Retes. "Arresto Domiciliario" was shot in Costa Rica. In 2007, she worked with her father in La Cadenita, an independent film directed by him. In 2010, while studying in NYC, she participated in A través del silencio, also directed by her father. Since then she has appeared in film and television roles in both the U.S. and Mexico.

In 2011, she was cast as "Mariana" in the Mexican teen-oriented drama series, Bienvenida Realidad. For the role, she learned to play the guitar. The show was based on the original Chilean version of the same name. The show explored topics including sexuality, drug abuse, and eating disorders. Sofia's character was bisexual. The series had one season with 120 episodes. It aired weeknights in Mexico and in the United States on MTV Tr3s.

Sisniega's late father was Marcel Sisniega Campbell, a Grandmaster chess player, Writer, Screenwriter and independent film Director. He died on January 19, 2013 from a stroke. Her paternal uncle, Ivar Sisniega, is a modern Pentathlete and Politician who competed in the Summer Olympic Games in the 1980s.

Sisniega is an animal-rights Activist and vegetarian. In her spare time, she rescues animals and assists with putting them up for adoption. She currently lives between Mexico City and Los Angeles. She speaks Spanish and English In August 2014, she founded, "Milk Bar", a bakery featuring organic, vegan and gluten-free cookies and desserts, located in Mexico City. In March 2015, she partnered with actresses, Zuria Vega and Marimar Vega, to expand the bakery, changing its name to "Milkella by Milk Bar".