tell her to have a break from him to get her head round this. firstly like you said rebound is a huge issue. In her break she should look at her life what future goals she wants or where she is headed.
If she can see the man being a part of her life, then she should first help him convert to Islam. Also his immigration status will have a major effect you have to show her it is not going to be easy. if she is having doubts at this early stage then they probably are there for a good reason. Also what would her family say???