When she loses her mercantile’s postal permit to a jealous neighbor, a young woman must find another way to keep the store open during the Depression.

What is the specific method that she is going to use to keep the shop alive? That should be the driving goal for the second half of the logline, as we need a specific thing to picture when we're visualising the story.

Jealous neighbour feels vague, what is she jealous about?

Think visually, what information does a reader need to picture the story you have in mind? We can't film internal struggles, only physical actions.

The bones are there, it just needs detail.