I read a book when I was 9 in 2012 with a character named Violet. She and a boy went to the library to research something. They also went to the forest.

[Pony]

I'm just going to throw out a random book, solely based on the girl being named Violet.
The Bad Beginning? Or one of the other books of that series?

[Spellbound_Rose]

Something from The Boxcar Children series? There is a character named Violet. As for the forest, it wouldn't be beyond the series, but there are a lot of books. I mean, they do find a boxcar, but i am assuming that it is a smaller object.

Most of the books are mysteries.