My Voice Instructor?

I guess it depends on the quality of your instructor. If she has a program that is systematically developing your vocal skills, you should sing what she tells you. As your singing improves, you can bring more to the kind of songs you love. But if she just doesn't like (or isn't familiar) with the songs you love, and she is picking other songs because they are easier for her, or more familiar, then I would insist. You are paying for her expertise, so use it where it does your singing the most good.