First up. In many ways I liked the story. Except when I think back after reading, I go hmmmmm, not in a good way.
The sentence structure is a bit unique. Short one action sentences. At first I thought it was a bit staccato, yet it did seem to fit how a 100 year old ghost might feel. Simple thoughts as if being alone for so long left her incapable of complex anything. So although the sentence structure was off putting in the beginning, it actually gave a rhythm to the story that worked.
SPOILERS SPOILERS SPOILERS SPOILERS SPOILERS SPOILERS.
My main issues with the story are more along the lines of universe creation. Ellie has been dead for a hundred years yet uses words and phrases of a modern girl. Given the foggy nature of most of her thoughts, this creates an incongruency within the story. While she mentions that the house has been in the family since she died, nothing is mentioned of the people within her house only the boy next door. Where did Ellie's jealousy come from? It doesn't fit, although necessary to the story, it feels wrong. How did Mason carry so many boxes? Why would he carry boxes? Why would his sister write him a letter? Why not to their mother? How did Mason know so much more than Ellie about being a ghost? There are many many other questions, but these are the most important.
While the story's premise is quite interesting, the universe building needs work. There are too many scenes that feel false within the story to make it satisfying. I had too many "I don't think so" moments while reading it.