Although Myrna was born and raised in the Los Angeles area, she hardly noticed it as a child. She spent most of her childhood in Tijuana, Baja California, with her grandmother or at the family ranch in Acton, California. In her early teens, her family moved to the quiet suburbs of Santa Clarita, where, out of boredom, Myrna turned to rock music and the stage. She studied dance for many years but never found the exact creative expression she was looking for; she found herself reading plays aloud in her room. Although it was completely clear that acting was her first love, she had many doubts about her ability to "break through" in the field, and she decided to go to college as a creative writing major. By her senior year, when asked what she wanted her thesis to be, the only answer she could give was: "Acting." Myrna gave up her college degree to devote herself entirely to a career in the rapidly growing film industry that was right on her doorstep.

From the very beginning, she had many commercial successes: she appeared alongside will.i.am in a Coca-Cola advertising campaign, and she also showcases her Mexican roots in several campaigns for the Hispanic market, from McDonald's to Chevy. In theater and film, Myrna has been fortunate to work on diverse roles in both movies and television. She has been everything from an armed bandit to a shy bride, from a nerdy girl at a burger joint to a spoiled high school drama queen.