Sainz was raised in Santander, a port city on Spain’s north coast in the Cantabria region. She later moved to Suances, also in Cantabria. "The first time I saw her, when she came, I realized her virtues. She was a girl with a lot of energy, with a lot of desire. From the beginning, I saw her a dancer,” Sainz' teacher, Marta Rojo, told "El Espanol". Rojo remembered that Sainz started formal dance training in 2010. 