I feel like I'm being psychically attacked here.
I don't need to tell you all that SU's music is way more than "pawing at a piano" or beatboxing or dubstep... Because we all have ears. Like it's clear she's never watched any meaningful amount of show and it pains me because of how obvious it is.
So I'll sperg on the term leitmotif and how Undertale has ruined the term somewhat. These days we define the phrase as being a melody that defines a specific character. And while SU has these (Stronger Than You is the most prevalent), it more relies on the instrument and rhythms used. It's more like Homestuck than anything, and there is some cross contamination between the two.
But, The Diamonds have a concrete example listed in the first art book. They each have an associated musical chord (a Minor 7th chord), and we hear it whenever they're mentioned. White is on the 5th scale degree, Blue and Yellow are on the 4th, and Pink is on the 3rd. There is a world of autism I could go into, but I am trying me best to restrain myself. The Diamond theme is also played on this weird melodica sounding instrument. It feels synthesized and fake, but this makes it very easy to pick out in anything it's in.
You can hear it here best. Listen as the character hits each diamond on the console. Yellow and Blue are almost the same, but they're rearticulated to show they're also different. There's also a difference in notes to aurally show the difference but Lily hasn't put in work then I won't either. I don't even know where my art book copy is, this is all from the crack of my ass.
And...just gosh Lily's not very musically inclined. I was listening to something on taste, and the video brought up being able to dissect the music with our ears, and being able to isolate different tracks of music to know what works and doesn't work. The more she talks about music, the more it reads like she wants to be into music but she hasn't put in the time or effort or resources or education... I mean, if she were musically inclined she would know how saying that the SU music doesn't have a melody is shockingly ignorant.