She began acting at the age of six. In her first starring role, she played the role of Patsy in the movie Ernest Saves Christmas in 1988. In 1989-1996, she was cast as a Mouseketeer in The Disney Channel's All-New revival of the Mickey Mouse Club (later known as MMC), on which she remained until the show was canceled in 1994. Two years after the show ended, Alley graduated from Lakeland Senior High School in 1996. Alley continued her education at the University of Missouri, receiving her Bachelor of Arts in theater with honors in 2000.

Alley also had a brief stint in an on-screen character role of Lisa Seltzer on The New TNN's roller derby program WSL RollerJam in 2002 from midway through the season to the end of the series.

Alley appeared in her own play, a one-woman show titled Look, Ma...No Ears! (A Show for One-Woman and the Voices in Her Head), a play on which she collaborated with Robert Stein and Stephen Winer. The play, directed by Ben Rimalower, premiered in April 2006.

Alley appeared in the World Premiere production of the musical "Having It All" at the NoHo Arts Center in Los Angeles in 2011, for which she received an Ovation Award nomination for Best Actress in a Leading Role. She reprised the role in the Laguna Playhouse production in March of their 2013 season. In the same year she appeared on the How I Met Your Mother episode "No Questions Asked".