Reddit reviews The Complete Idiot's Guide to Singing

Have you tried talking to her about it? That would be the best place to start. If you live in a college dorm, your RA should be able to do something about this. If they can't, file a noise complaint with campus/local police. This is in their jurisdiction, and you are probably not the only one annoyed by her singing. You could also be passive-aggressive and buy her a book on learning to sing. If you have taken the calm conventional routes, multiple times, and it hasn't stopped, I suggest you get creative:

Record her singing. Post it to social media where she has an account. Tag her. Write a complaint about her in the accompanying text post.

OR

You could start a war of attrition. Play your music at what you think is an appropriate level, ideally when her music isn't playing. If she complains, turn up the volume. If she puts on her music, drown it out. If this doesn't break her, find music that you still like but that she would find more obnoxious and repeat the steps. If this still doesn't work, you might consider the nuclear option. I found this loop particularly annoying, but you know her better. You mentioned she likes Disney music. This is good, as it means she likely has several fandoms she loves, but more importantly, it means she has several fandoms that she hates. Find a 10 hour loop from one of them. Blast it at full volume whenever she blares her music. You could also go the route of blasting the most obnoxious, awkward porn you can find.

Still failing this, you could always move out as a last resort, but it would be pretty shitty to have to move out because of a bad roommate's easily fixable behavior.

Let us know how it goes, and good luck! 👍