You can indeed major in anything you want. It appears that the largest group of students major in biology, but that is probably mostly either because it is what they think of, or because there is a large overlap between the required premed courses and the courses required for a biology degree. Here is a web page from the AMA about the subject. As a former math major, I was interested to see that 168 of the students they tracked were math majors and then went to medical school.
One thing that you could do is to pick a couple of universities that you otherwise might be interested in, and see what the required courses are for a degree in music therapy. Also see what the required courses are for premed. Then see whether you could fit both into a four year course load. Remember that you can take classes over the summer. Both of my daughters got at least some academic credit for courses or for research that they did over the summer while they were undergraduate students. This made it much easier to fit in every course that they needed or wanted in four years. One daughter was even paid for the summer research (getting money and academic credit at the same time) which made it quite affordable.
Veterinary school is not quite the same thing as medical school, but it is similar and the requirements overlap quite a bit. One daughter graduated with her bachelor’s degree one course short of what she needed to apply to DVM programs. She took the course at community college while working as a vet tech, and then applied to DVM programs with a very high success rate.
Personally to me “music therapy plus premed requirements” sounds like it really should be possible.