This story is wonderful, I must admit I never saw the ending coming. It took me completely by surprise, and I think that is what I find the most appealing about it.
Read the story now
You had several good elements of the horror story worked in, such as the common, ordinary life interrupted by a catastrophic, unforeseen event, the drastic actions the main character is willing to take, and, of course, the repercussions of those actions. However, the wording is very brief and blunt, pushing the story on at a rather rapid pace, but I admit those particular aspects may be intentional as it is your style, and horror stories need to move quickly. Your grammar and sentence structure need a little work though, seeing as there were points in the story that the wording was a little confusing because of the text effects and the brief, fragmented way it was described.
I found this to be primarily in the letter when Agnes read it, the rest of the story looked pretty good and was easy to follow. I would recommend just slowing yourself down a little when you're typing things up and proofreading before submitting, so that you know you have your wording correct, and you know that your punctuation and grammar are right (though I struggle with grammar too, so it's alright).
All in all, wonderful story! I enjoyed it immensely.