You could start by finding out the reasons behind her reluctance. Maybe she doesn't like the types of stories that are usually shown at the cinema. Try to find a movie that is based on a genre she loves, like a romantic comedy if she likes that sort of thing. You can also make the cinema experience more appealing. For example, plan a whole day around it, have a nice meal before or after the movie.
One thing you can do is to involve her in the movie - choosing process. Let her know that there are a wide variety of cinema stories out there. If she likes action - packed adventures, look for movies with exciting stunts and a great story line. Also, you can offer to go to a special screening, like a midnight showing or a director's cut, which might make the whole thing seem more exclusive and interesting to her.