I love this story so far. It's the type of thing that's been done before - a person rereading an old letter. But the way you do it makes it original and interesting. I love the sentence that says she's reading the letter for comfort and not because of the context. That kind of makes you think, because it's the type of thing I had never thought of before, but when you read it you think, "Why hadn't I thought of that before?" This is fantastic.
Other than that I enjoyed it, didn’t spot any grammar or spelling mistakes.