Resbala comes from the verb resbalar, which literally means "to slip" or "to slide". However, in this song, Lola Indigo uses the very common colloquial phrase "a mí me resbala".
This expression idiomatically means "I don't care" or "it's like water off a duck's back." She sings, "Ahora me está llamando, a mí me resbala" (Now he's calling me, I don't care), perfectly capturing her indifference to her old crush. It's a sassy and powerful way to say that his attempts to get her attention simply slide off her without any effect.
Have you ever had an old school crush who completely ignored you, only to come running back years later? That is exactly the kind of sweet payback Spanish star Lola Indigo dishes out in "Niña De La Escuela" alongside TINI and Belinda. The whole track revolves around a massive glow-up. She rubs it in right from the chorus: "Soy aquella niña de la escuela / La que no te gustaba, ¿me recuerdas?" ("I'm that schoolgirl / The one you didn't like, remember me?"). Now that she has polished her diamond ("pulí mi diamante"), the tables have completely turned, and her old crush is left drooling in regret.
The song is packed with cheeky, direct brush-offs that are great for learning real conversational Spanish. When she tells him "Límpiate la baba que se te cayó" ("Wipe up the drool that fell"), she is mocking how stunned he looks. Belinda even drops a hilarious pop-culture punchline: "Baja de la nube que no eres Goku" ("Come down from your cloud, you aren't Goku"). It uses the Spanish idiom estar en una nube (to have your head in the clouds or act too proud) while poking fun at the Flying Nimbus cloud from the anime Dragon Ball. The message is completely blunt: you had your chance back in the classroom, and you blew it!