What's the Name of That Book??? discussion

I probably read the book between 2011 and 2014, so it shouldn't be any newer.
In general, the book was about the protagonist's mental problems. Maybe also self-harm, but I'm not quite sure anymore.

The only thing I remember is that the older sister dies on the train because of a terrorist attack(?). They both get on the train, but the protagonist survives. Since then she has felt guilty because they only took this train and not a train earlier because of her (she still had to tie her sneakers or something like that).

Unfortunately, I don't know any more, but I hope someone here has also read the book.

Lost for Words by Alice Kuipers? It was also published with the title The Worst Thing She Ever Did.

Some Goodreads reviewers describe Lost for Words by Alice Kuipers - Rainbowheart's suggestion:

- "Having lost her older sister recently in a tragic bombing whilst travelling to the National Gallery on a train, Sophie finds herself struggling with her loss and, after it was suggested by a councillor, begins writing her thoughts about the present and her memories of Emily in a journal."
- "As the story unfolds, Sophie slowly reveals the events of the previous summer with her shoe laces, the train, her sister, Emily, and the aftermath."