"Niña Mía" is Elsa y Elmar talking straight to a girl, maybe her younger self, maybe a daughter, and it opens with a promise: "Yo te cuido, ve y camínate la vida" (I've got you, go and walk your life). It's a lullaby for growing up. She knows the girl feels "sola y perdida" (alone and lost), and her answer is simple: "tú tranquila" (easy, stay calm), that day will pass.
The advice gets surprisingly specific. Don't believe your own head when it says you don't deserve what you built. Trust the tight feeling in your chest, "porque buenas intenciones no hay en todos lados" (because good intentions aren't everywhere). Then comes the bit that stings: "Ríe cuanto puedas porque llorarás, ama hasta que duela porque dolerá" (laugh as much as you can because you will cry, love until it hurts because it will hurt). She even tells her to thank the person who breaks her heart, and the last line is a lovely bit of grace: if you look back, "que sea solo pa' saludar" (let it only be to say hi). Learner tip: "pa'" is the spoken short form of "para", and the song is packed with the future tense (llorarás, aprenderás, despedirás), perfect for practice.