Sad book

"Megume and the Trees" by Sarah Toshiko Hasu is about an Asian-American girl who lives with her dad, "evil" step mom, and little brother. One day, she is coming home and swears she hears her dog barking in the woods. The problem is that her dog was sent to pound long ago and is most likely dead. Deciding that the barking was really her lost dog, she charges into the woods, chasing it. Eventually she catches the dog which turns out to be her dog. The story follows Megume as she attempts to find her way out of the forest. As she moves through the forest, she encounters unusual events and scenes such as a lost boy that reminds her of her brother, a Japanese style house, a bombing raid from WWII, her long dead grandfather, and the like. She eventually finds her way out by following a river. The story ends kind of on a sad note. Throughout the story are copies of letters from Megume's bestie, Emiko who happens to be in France at the moment. The letters start out happy and perky but start turning sad until eventually, the final letter. This letter helps explain everything. I know Megume is okay, but feel very sad for Emiko in the end.