Huellas literally means "prints" or "traces," like footprints or fingerprints. It's a beautifully evocative word with a lot of depth.
In this song, KAROL G uses it metaphorically to deliver a powerful message to her ex's new lover. She sings "Cada que te acaricie, tu piel ya tendrá mis huellas" (Every time she caresses you, your skin will already have my marks), meaning her impact on him is permanent and she can never be truly erased or forgotten.
Colombian reggaeton star KAROL G flips the usual breakup script in "A Ella". Instead of pleading with her cheating ex, she turns her attention directly to the other woman. Right out of the gate, she shuts down any conversation with him: "Tú no te mereces nada, no estoy hablando contigo" [You don't deserve anything, I'm not talking to you]. The verses build a sharp comparison between what both women brought to the table. She gave everything and planned for the long haul, while the other woman was merely a quick thrill: "Ella es un segundo y yo era para siempre / Algo pasajero te condenó a perderme" [She is a second and I was forever / Something fleeting condemned you to lose me]. In Spanish, using pasajero literally means "passenger," but here it acts as an adjective meaning temporary or passing by.
What makes the track stick is how KAROL G refuses to act defeated. She mocks the idea that physical looks give someone the right to take a partner: "Que se cree que por bella, ella / Puede robarme todo lo que nunca tuvo" [She thinks that because she's pretty, she can steal everything she never had]. Then she delivers two cold realities. First, her history with him cannot be erased: "tu piel ya tendrá mis huellas" [your skin will already have my fingerprints/marks]. Second, she drops a warning about karma. She warns the new woman that a partner who betrays one person will repeat the pattern: "Que si fue así conmigo / También lo será con ella" [If he was like this with me, he will also be like this with her].