I can tell you from experience that being cheated on really takes a toll on one's willingness to open up and to trust. It leaves a LOT of emotional scars, especially if the relationship was serious. It will probably take more than five months to get her to be able to reciprocate feelings in the same way, especially with the wounds being this fresh.
Basically, you have to be willing to put the time in, and hope she comes around. No guarantees, though. Sometimes these sorts are better off just being left alone until they feel they are ready to be in a relationship again.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi