You can't do more than you have done alone. You need to encourage her to find mental health care in this state or hers. This may have nothing to do with you or her. She may have a mood disturbance that can't be remedied by having a happy relationship or by finding happiness on her own. There has to be an intervention when she or others that love her are not enough. She needs to find a proactive choice that can address her problem. Sometimes people think that by moving or getting a new car or finding a new love changes who they are or makes them happy when in fact the depression does not respond to such things. When you move your emotions go with you. Encourage her to find care. Then she may return with a new outlook instead of returning with this same problem.
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