This is nicely written, and free of technical flaws, but the characterization of Lacey, the most important part of the story, doesn't come off. I would say that the meat of the problem lies in this:
“I can’t stay here anymore, Janie.”
“But- the quarantine. We have to.”
“They can’t stop us if we just drive.”
“I’ve never been further than Provo, Lacey. Where would we go?”
“Someplace nobody knows us. I want to see who I am when no one else is around. I think I met
her in the desert. I think I liked her.”
Your main character, who is also the narrator, is announcing a change in herself. That's not forbidden, but there wasn't enough build-up to it. A young woman who went through what Lacey did should have reflected over it internally to a greater degree than you allowed her. Another way of putting it would be to say that you favored the external action of the story somewhat too greatly over the internal development of your main character.
However, I have to give you big points for a smooth style and capable handling of an unusual setting for a post-apocalyptic story. That subgenre of SF is pretty badly glutted, and the stories tend to resemble one another far too strongly. Yours doesn't have that problem.
A suggestion: Find a copy of Harlan Ellison's old "Dangerous Visious" anthology and read Henry Slesar's story "Ersatz." I promise you'll get a chill out of it, at the very least!
(review of free book)