Mayberry was more of a concept than a precisely located town. It represented a certain kind of charm and simplicity in the imagination. So, it's hard to pinpoint an exact geographical location.
Since erotica is not in line with the positive image of Mayberry, there are no such 'famous' stories in this regard. The focus should be on the positive and moral stories from Mayberry that can bring positive impacts and good feelings to the readers.
Well, Mayberry is purely fictional, so it doesn't have an actual geographical location. It exists only in the imagination of the creators and the stories it's a part of.
I haven't read the 'Martha Martha' short story specifically. But generally, when analyzing a short story, we can start from aspects like the characters. Maybe Martha is the main character and we can look at her personality traits, her goals and desires. Another aspect could be the plot. Is it a linear plot or does it have flashbacks? For example, if it's about Martha's journey, whether it has a clear beginning, middle and end in terms of her experiences.
In many Martha May x Grinch fanfics, the theme of transformation is often present. The Grinch, who was once a bitter character, starts to change for the better because of Martha May. Also, the theme of acceptance - both Martha May accepting the Grinch as he is and vice versa - is quite common. These themes help to build an interesting and often heart - warming story.