My D had a thriving studio during and after grad school. She got most of her referrals through her MM school of music. People calling the U for teachers. And in grad school she worked as a VP teacher at a well known private drama school in LA. She got student referrals through them as well. Before she moved to Europe she had more students than she needed. So your D needs to start thinking about possibly going to a highly reputable grad school where VP teachers well taught and in a market where are sought after and where they make a decent hourly for private lessons. (for D that was between $85-$100 per lesson) Possibly focus on this rather than a double major?