Hey Dan,
Sorry to hear about the problems you're having. My suggestion would be that you focus on your own weight loss and not bug her about it. It's really easy to become too much of a "cheerleader" for weight loss when you're the one losing, and it's rarely appreciated by people who are still struggling with taking that first step.
Try to encourage her, but just as an example, don't try to drag her to the gym with you. If she wants to go to the gym, she should go by herself and work out by herself, without being under your watchful eye. And by all means, don't get hypercritical of what she's eating or start asking her a bunch of investigation questions about how much, what, and where. You're not the food police.
It's possible that your relationship won't survive the challenge of you losing and her not losing--but again, focus on yourself. Don't express your disappointment with her. That's really not cool. Work on your own weight loss, and be cheerful and supportive without being insistent or trying to get her to do "the right thing." Ask her if she wants to lose weight, and if she says yes, ask her what you could do to help. Don't
tell her what you think she should do, ask her what she thinks you could do. It may be that the answer is "Leave me alone."
For what it's worth!
Jay