Mother with severe back problems and depression won't take her Prozac. Any advice?

My mom is 68, in okay health except for severe back problems and severe depression/anxiety. Her back problems have escalated to the point where she can't get out of bed. She is 2 hours from any major hospital. I'm 9 hours away. Her developmentally disabled brother lives with her and is caring for her. The pain and being bed bound have made the depressing/anxiety much worse. She is calling and ambulance to take her to the ER several times a week, mostly because of severe constipation from the pain meds and lack of movement, where they do nothing. I found out today she was prescribed Prozac by her family doctor but is not taking it because to quote her "her problems are physical not in her head". Any advice for me?