Boyfriend hasn't seen her over a week and broke a promise?

He is working on night shifts as a Doctor while my cousin works as a Teacher and as a karate instructor during the evening. They have been together for over 3 years. They haven't been able to seen each other other a weekdays and on the weekend he works during the day for the past month. Her boyfriend promise her that he will see her on her birthday. She was happy that he would be able to take the time to see her but when her birthday came she went to the office and she receive her favorite flowers from him. She was really happy when she came to the class room but when she open the letter that received with the flowers it says that he couldn't be able to be there for her on her birthday. She started crying and her students look worried. They had a fight and now she is at my house for the weekend. Do you think it is just a misunderstanding and her boyfriend really cares about her because I talk to him over the phone and he said that he was sorry and explained why he couldn't be there. He said that he is working over time to get a wedding ring for her. I was shock at what he said and he told me not to tell her anything. He wants to see her on Sunday evening at the park. Now with my cousin, how do I tell her to get together with him because she refuse to even see or talk to him. She is a stubborn as a mule and I want to get her together with him. Should I lie and plot a trick to make her see her?