It sounds like your effort to eat better and work out are strictly self motivated. Good for you, not many people have the initiative or willpower to do this on their own. However, if you are able to incorporate this into your relationship and make it something you do together, maybe you could build off this and make it a step forward. It might not be such a good thing to have somebody so dependent on somebody else to help themselves, but I'm trying to exercise all the options here. It can help you guys spend more time together and bond together doing something besides sitting around the house or whatever. Get gym memberships together and try and find times that fit for the both of you, make menus together of healthy foods for the week and even if you have to do the cooking and shopping, if she is working with you it will be worth it. At least to kick start it, maybe she will really take to it.
Having a healthy lifestyle is a big thing. To start and to be consistent with it. To make time for working out takes some rearranging of her time along with cooking good healthy things. Maybe you can help her try and shoulder this load by working as it as something together, but if she's flat out adamant against doing it, there isn't much you can do. Try everything you can, but if she is going to throw a fit about it and act like she's a victim to her genetic traits or something, you are going to have to tell her that it's interfering with your attraction to her.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.