I know where Miley is coming from. I used to be among the "I hate musicals" brigade many years ago. Ironic too, since I have loved all types of music for years and am have been an amateur musician for most of my life.
Anyway, I got a bit older and a little more mature and open minded and most importantly, finally happened to catch a musical on T.V. whose songs I liked a lot. That's when realized that not all musicals were the same and that as long as I liked the songs, I could really like "musicals".
Miley may find out as she matures that there likely will always be some musicals out there she doesn't like, but that there are some she can like.
OTOH, maybe she is uncomfortable with seeing that there are lots of kids out there around her age who are much better singers than she (except the dude who plays "Phin").