I agree with Shawn - all three areas can offer meaningful and rewarding career options. However, they don't have to be mutually exclusive, and all of them provide opportunities to help people.
For example, you might consider becoming an attorney who specializes in legal issues affecting children, including adoption, access to special education, or child protection, to name just a few. Many people combine a strong interest in economics and finance with a law degree. You could study economics and finance in college and then pursue a graduate degree in those fields, or in medicine, or in law. (Some very hard-working and dedicated people pursue more than one graduate degree).
Or you could consider a career in one field and do volunteer work in another. Many people do that and it can be an excellent way to build new skills and meet new people.
I also agree with Shawn that what's ideal is being able to do work that gives you a sense of purpose and satisfaction. So this is a good time to think about what you know you do and don't enjoy doing, and also to talk to friends, family and teachers about how they chose their careers and what they enjoy the most about what they do. It's great that you have an opportunity to shadow someone who works in one or more of these fields. Pick the one that interests you most right now - no matter what, it will be a learning experience.