I say, Follow your heart. Here are my thoughts as someone who grew up with a non-mormon father and as someone who free a non-mormon dating. When I site to him about this he seems to agree that he doesn't like the person he's becoming and doesn't look forward to a career in medicine, but says datng can't leave medicine.
While Scientology is way worse hopefully the parallels will get her thinking. And that fairly constant theme has some deep implications your girlfriend will have to face.