In the summer of ’93 Larisa (age 12) auditioned for and got the role of Alex Mack in the show "The Secret World of Alex Mack". Co-creator and producer Thomas Lynch described her audition as follows: "We looked at 400 to 500 people. She came in and auditioned and was quite tentative with the material. But we liked her smile and asked her to read again. This time she relaxed and nailed it. She has a real awareness of the innocence of being a young teen".

"The Secret World of Alex Mack" was shot in a converted warehouse in Valencia California which is located about an hour from Los Angeles. For the first season 13 episodes were shot in August 1994 when Larisa was on vacation from school. The second season episodes (26 total) and third season episodes (30 total ) were made in the summer and well into the school year. This meant some big changes and sacrifices for Larisa in 1995 and 1996. When the show was being made Larisa commuted regularly from her family's home in suburban San Francisco to Los Angeles and a two-bedroom rental apartment that she shared with her mother (she flew back to San Francisco on weekends). While she was in LA she missed her dad, her friends, and her cat Tigger. During the time she was in LA when school was in session she also had to work with a tutor as well as work on the show. Concerning this Larisa said "It's hard, 'cause we're supposed to do three hours of class a day on the set but we can only do it in 20-minute increments. So it's like, I'm doing a scene, then they rush me back and I'm doing geometry. I don't really get much time to focus on either one." Her work day lasted nine and a half hours and she usually had to be up at 5 AM. On some days after work she would then attend acting class.

Although there was hard work and sacrifice involved in making "The Secret World of Alex Mack" there were also great accomplishments and great times. The show was very successful, bringing the Nickelodeon cable network some of its highest ratings ever (it was seen by nearly two and a half million viewers a week) and Larisa received the most fan mail ever. The show was also praised by television critics. Larisa spoke often about the great people she met while making the show including costars Meredith Bishop and Darris Love. Larisa has also talked about the fun she had making the show. She said (while giggling) "I get a chance to be a kid on the set. We all sort of run around and goof off and are total spazzes most of the time."