You need to lead by example. If you cannot lead by example, it will not happen.

You need to start adopting a healthier lifestyle and pick the places you go to eat with more healthier options.

If you opted for the healthier food, she will indirectly follows. If you opted for more frequent of walk at the park or housing area, she will follows.

The most importance turning point to push it to self sustain momentum = she must be able to see the changes happening to her body, her waist line reduces, she can wear more attractive clothing with more confident.

That is usually 6~9 months gestation period. If you cannot endure pass this period, usually the subject will be demotivated & loss the momentum.