Does she want to lose weight? If not, don't pressure or try to trick her into doing so. I've had that happen to me for a long time, and it does the exact opposite of "motivation". I'm obviously not saying that you are doing these things, just be careful in how you approach it. It's good that you realize what a risk it is, and it's GREAT that you are looking specifically to find good ways to avoid pressuring her.
For specific recommendations:
- Be more active, invite her to come along when you do things.
- Respond positively to any active activities she suggests.
- Eat healthier and offer to split meals with her, so that you can reduce your own intake, and she'll be helping YOU, instead of feeling like you are pressuring her. Don't be surprised if she gets excited about it at that point.
- Answer her questions honestly. If she wants to talk about your loss or your plans, goals, etc. then talk about them.
- Have a good time with her, even if she isn't interested in "dieting"; if she's overweight, she knows it, but may have tried and failed to lose weight many times. If that's the case, it's almost guaranteed to be a sensitive spot for her.
- Talk about your own food plan and exercise, without putting any pressure on her to join in. Just remember it is sensitive for some folks.
How much walking do you already engage in? For example, is there a store within walking distance? If you need to make a quick trip to the store, walking to the close one can be a lot better for you than driving or riding the bus to one that is farther away, even if the price might be slightly higher at the local store, and the gas/bus fare might make the difference on small trips.
Obviously, big shopping trips would be better to drive, but they are their own kind of exercise
I hope those ideas help!