Law firms are owned by the partners of the firm. In the United States, all law firms must be partnerships or sole proprietorships and all the partners or owners must be lawyers. Non-lawyers are not allowed to have any ownership interest in a law firm, with rare exceptions, such as for widows of deceased lawyers, and they are usually required to sell the partnership interest back to the firm. So you need a law degree to become an owner of a law firm.
If you have a law degree, there are three ways I can think of to become an owner of a law firm. First, you can get hired as an associate. This is usually how law firms hire attorneys straight out of law school. Associates will work at the law firm as an employee, not an owner. If an associate works at the law firm for about seven years and impresses the partners with his or her skills, she may be promoted to becoming a partner and will buy an ownership interest in the law firm. Second, you can become a partner at one law firm, and be hired as a partner at a different law firm, without having to be an associate at the new law firm first. Usually, very successful lawyers who will bring good paying clients to the new firm have the most chances to do this. Third, you could start your own law firm. This is the easiest way to own your own law firm, but it's the most risky, since you have to start everything from scratch.
Law firm partners' pay depends on how large the firm is and how successful the lawyer is. A successful partner in a large law firm in a large city could make a million dollars a year, while a struggling solo practitioner may have trouble making ends meet.
Basically, any means of becoming an owner of a law firm requires a lot of hard work over a long period of time. It's not something you can achieve simply by taking the right classes in college.
You can still WORK at a law firm if you are not a lawyer, as most law firms will have some secretaries, paralegals, and other administrative assistants on their payroll, but they will never be allowed to own the law firm unless they become attorneys.
If your parents both agree, this would be legal.
However, if they're divorced, this is a valid reason to change custody to the other parent, who most likely has no intention of paying child support for you to move in with strangers.
the least probable thing is that this friend has even talked about this with her parents.