Winning the award in the competition “El rostro de El Heraldo de México” in 1997, she participated in the soap opera La Usurpadora. Fonseca had an important role in the soap opera Rosalinda playing the little sister of Rosalinda, Lucy.
She had her first protagonistic role in the soap opera Amigos Por Siempre next to Ernesto LaGuardia. She combined this soap opera with a theater performance Mama nos quita los novios with famous personalities such as Angelica Maria, Hulio Aleman. In 1999, Fonseca appeared in soap operas such as Gotita de amor and Preciosa but the role of Rosalinda’s sister gave her the most exposure. Fonseca then starred with René Strickler in a ten-episode soap opera called Mujer Bonita. At 1998’s Premios Lo Nuestro,[clarification needed] she won the award for Rostro del Año.[clarification needed]
She has joined Telemundo’s network and is the main protagonist in Corazón Valiente, alongside Ximena Duque, Sonya Smith, and José Luis Reséndez.