De Montecristo was born in Olocuilta, La Paz. When she was ten years old, her family left El Salvador and settled in Las Vegas, Nevada.
In 2013, de Montecristo auditioned in Los Angeles to be a part of Nuestra Belleza Latina 2013, a pan-Latina beauty pageant reality show broadcast on Univision. During the competition, her mentor was Venezuelan Osmel Sousa. She was ultimately selected as one of the twelve finalists and progressed each week until being declared as the winner.
De Montecristo became the first woman from El Salvador to win the competition, in addition to being only the second Central American after Nastassja Bolívar of Nicaragua won Nuestra Belleza Latina 2011. Following her win, she was awarded $250,000, a new Kia Forte, and a year-long television presenting contract with Univision.
Following her reign as Nuestra Belleza Latina 2013, de Montecristo had planned to take part in Nuestra Belleza El Salvador 2015 competition. However, she dropped out following comments against Mexican immigrants said by Donald Trump, who owned the Miss Universe Organization at the time, which the winner of Nuestra Belleza El Salvador went on to compete in.
After Trump sold the organization to WME-IMG, de Montecristo announced that she'd compete in the Miss El Salvador 2018 competition. She won and was crowned Miss El Salvador 2018. She will now represent El Salvador at Miss Universe 2018.