If you want to save yourself some stress and have any kind of musical aptitude, I'd suggest some passive learning. Like get away from the game for a while, listen to audio of the song with the chimes included while doing other stuff, and then you will just learn how it goes and be used to the tempo changes. Since the entire battle (save for the last couple of notes) is all simon says, you will be much better equipped to deal with it when you're able to predict what's coming.
The biggest barrier to defeating this boss, aside from the troll notes at the end, is that one miss = fail. The parts you hear a lot and memorize are unfortunately the easy early parts, so it's really easy to choke once you've gotten to the very last segment.
Also, the visuals are just there to confuse you. If you can keep the beat even by tapping the finger of your other hand while the intoner does her bit, it will be easier to repeat what she does.