Risueña translates to "smiling" or "cheerful," but it carries a more nuanced and endearing connotation than a simple "happy."
In the context of Mon Laferte's "El Cristal," the singer observes her beloved through a pane of glass, noting, "Te veo risueña" (I see you smiling/cheerful). This word beautifully captures the gentle, almost wistful joy of seeing someone you adore in a state of natural happiness, even when you can't fully reach them. It's a less common and more evocative way to describe someone's pleasant demeanor.
Mon Laferte builds "El Cristal" around one image she won't let go of: a sheet of glass standing between her and someone she can see but never touch. She opens watching them sleep, "Te ves tan bella" ("You look so beautiful"), and the tenderness turns to frustration inside a single breath: "Quiero abrazarte" ("I want to hug you"), immediately followed by admitting she can't, because of that same glass. The song never says what the glass actually is, which is what lets it read as memory just as easily as distance.
Three times, the chorus turns that barrier into a goodbye: "Es a través de este cristal" ("It's through this glass"), each repeat landing with less hope that the glass will ever come down. By the closing verses she's not reaching for the person anymore, just watching them: "risueña" ("smiling"), "serena" ("serene"), the kind of close attention people pay to something they're about to lose for good.