Keena went on to portray the character Bertha in a stage reading of Strindberg's The Father with Al Pacino, and had her first starring role playing Snow White against Sigourney Weaver's wicked queen in the folktale-inspired Snow White: A Tale of Terror. She has appeared in numerous television and movie projects including the TBS Original Movie First Daughter and Crime and Punishment in Suburbia which appeared at the 2000 Sundance Film Festival.

Monica appeared in the film While You Were Sleeping with Sandra Bullock, The Simian Line with Harry Connick Jr. and Lynn Redgrave, and Bad Girls From Valley High with Julie Benz and Jonathan Brandis in his final film role before his death in 2003 (the film was eventually released straight to DVD in 2005). In 2003 she played the heroine, Lori Campbell, in Freddy vs. Jason. In 2006 she played Celia in the film Left in Darkness.

Keena had a recurring role as Abby Morgan on Dawson's Creek and a starring role on the short-lived Undecla