Whats wrong please help!?

My moms dog has been sick it started with her jaw and and then went to her hips and legs. Now she is to the point were she can barely stand up by her self. She is now losing hair, her legs are very swollen, she has the red spot under her skin on her belly, she trembles while sleeping and can barley move. Please help if you know anything. The vets cant figure it out.