18 with no choice

My friend is 18. She pays for her own car and she pays for her phone. But her parents wont let her do anything. They tell her she's not allowed to go places or hang with certain people. And I get that she lives under their roof, but she isnt allowed to make any decisions for herself. I keep telling her she can legally decide where she goes and who she goes with but she keeps saying her parents wont let her. What should I tell her and how can she explain to her parents shes old enough to decide when she hangs out with someone?