Millonaria translates to "millionaire", but in this emotional song, it has nothing to do with money.
Becky G sings to her late grandfather, "Yo era millonaria nomás con tenerlos" (I was a millionaire just by having them). She uses this powerful word to express that the love and time she spent with her grandparents was the most valuable treasure she could ever possess, making her feel incredibly rich. It's a beautiful metaphor for the true value of family.
This is a beautiful and very personal song from Becky G, written as a letter to her grandfather who has passed away. She sings directly to him, telling him, "Tu recuerdo aquí en mi alma siempre está" (Your memory is always here in my soul) and that she would give anything "Por sentirte y abrazarte una vez más" (To feel you and hug you one more time).
She describes how empty the family ranch feels without him and how her grandmother's "sonrisa ya no ha vuelto a ser igual" (smile has never been the same again). She remembers his advice to "Persigue tus sueños" (Chase your dreams) and tells him that the dreams she had as a little girl are now her reality. It's a sweet tribute that also touches on the pain of regret, as she recalls him saying they'd have more time to see each other, but "no fue así, ya no hubo más tiempo" (it wasn't like that, there was no more time).