My dad wont take my dog to the vet?

Please help me. Yesterday my brother was playing fetch with my dog and suddenly during the game she stopped running and lifted one leg up and tries not to use it. When she walks she limps with it and when she runs she only runs with three legs. My dad says she'll be fine, but Im not sure. She seems even more worse today, shes shaking her hips in a unusual way when she walks. I've tried to make her just relax and try not to walk on it as much as possible, but my mom makes her walk around the house and stuff. What should I do? I absolutely cant take her to the vet , because of my dad.