For a male having sex is a physical desire but for a female it is an emotional need. If she is not showing any interest in physical activity then she could be having some underline emotional issues which only she can revel. You need to self analyze yourself if you are able to satisfy her emotional needs. If you think you are able to then you discuss the issue with her and try to understand her problem. At last you may seek help from psychiatrist or a psychologist together who will help you in the process.