Wow. This is gorgeous. So sweet and sad and aching. It sounds like a good thing, really, the expiration of sadness, which means that from the start I was a little bit suspicious of that premise, I suspected I would be led to the opposite conclusion by the end. And then the line, "she can't stop smiling." It's simple, and innocuous, and certainly not as poetic as lines like "i've felt this heavy hand on my back for so long that it's almost like a friend." (Which is a gorgeous line, by the way.) But it really gets you--she can't stop smiling. she can't stop smiling. And we get this impression of a face frozen in glee, unable to take any other shape no matter how much its owner might want it to.
Part of what I love about your writing is that you can take these ordinary moments, like running into a friend in the produce section, and marry them seamlessly with the internal monologue, the inordinary narrative world in your (and/or the character's) head. You find the poetry in the ordinary, the feeling and the meaning, and you do that here as well.
(p.s. I still read your book out loud to myself sometimes. it lives on a shelf with all my other most-important-most-precious books.)