One can safely infer that the narrator is planning on going to Mexico in order to write. She is, after all, a writer, and in the story she's headed up to a remote cottage in the Carolina Mountains with the specific intention of doing a spot of writing.

Like a lot of writers, the narrator moves around an awful lot from place to place in search of inspiration. The Carolina Mountains are one such place; Mexico another. The narrator's sojourn in the mountains has been very useful to her from a writing standpoint in that she's managed to finish her current work. However, as she freely admits, she's deeply dissatisfied with it.

Nevertheless, now that she's got this particular book out of the way she's keen to start another one, preferably one that will actually satisfy her this time. But for that she needs Mexican material. This would suggest that she already has the kernel of an idea for her next book. As we've already seen, this is a writer who draws inspiration from her material surroundings. That being the case, she intends to head down South to Mexico at the earliest opportunity. There she will write her next book, but only if the conditions are favorable.