Radiante translates to "radiant" or "glowing." It's a beautiful and evocative word that describes someone who is shining with happiness, health, or beauty.
In the song, it's used to describe a woman who has overcome past hurts and is now thriving: "Se ve más radiante, dejó to' lo que le hizo mal" (She looks more radiant, she left behind everything that hurt her). This word perfectly captures her transformation and newfound self-worth, making it very enticing.
Nodal watches someone from the outside for the whole song. She has come through something bad and the change is physical: Se miró al espejo y la venda se quitó ("She looked in the mirror and the blindfold came off"). The blindfold is the point — nothing about her situation changed, only what she was finally willing to see. By the chorus it is obvious to everyone: Y ahora se nota que / Se volvió otra mujer ("And now you can tell that" / "She became another woman").
The title works as a small trick. Otra mujer is the phrase Mexican radio usually reserves for the other woman in a cheating song; here it means she has turned into a different woman altogether. The man who caused it gets one line and no name — Quien la dañó y no supo amar ("The one who hurt her and didn't know how to love") — before she stops dealing with him at all: Ella se lo dejó al karma ("She left him to karma"). Even her crying is described as something taken from her rather than something she did: No le queda una lágrima, un cabrón se las llevó ("She hasn't got a single tear left, a bastard took them all").