Symbolism, Imagery, Allegory
In addition to not being human, Laurel is set apart from her teenage peers by her love of old things, like her mom's guitar. As Laurel explains to David: "I found it in the attic. It used to be my mom's. She showed me the basic fingerings and I just kind of play by ear now" (17.48). She's been playing for around three years, and everyone who hears her thinks she's pretty decent, so we're going to go with that.
But there's more to Laurel's love for her mom's guitar than meets the eye. We're going to pause and unpack some of the associations for you.
While chilling with Laurel one time, David observes, "You're holding it so naturally. Like you really love it" (17.53). This is while David and Laurel are hanging out the first night her dad's in the hospital, when Laurel's kind of freaked out about learning she's a faerie and about her dad's health crisis. Laurel plays a song and sings for David, and she admits to feeling better afterward. We think, based on this, that the guitar symbolizes Laurel's connection to her parents, and to the human world more generally.
The fact that Laurel latched on to her mom's guitar makes us think that she has some creative needs, and the guitar provides a good outlet for that. It also makes her feel connected to her family. And it's a thoroughly human thing to do (if faeries have guitars, we don't know about it), showing that Laurel views herself as a human, and clings to that identification even when she finds out she's actually a faerie.