General

From what you've told, it doesn't sound like what she needs is a push. It sounds like she needs reassurance.

So find out what is meaningful to her and reassure her in that way. And do it as a natural occurrence.

For instance, if she likes touch, the next time you're in physical proximity, touch her and let it linger just a bit.

But as I said, it needs to be organic. If you just run over and start rubbing on her and that's way out of the ordinary for you, it'll do more harm than good.

YMMV.

Too many men think that all they have to do is make their SO know that they love their weight. But that is not the issue. The issue is, if she likes her weight. No matter how much you like her weight, that is not what counts. If you really love HER, and not her weight, all you can do is support any decision she makes. It's frustrating, because if you know enough fat people, you know that dieting causes weight gain in the long run, which can make her uphappier.