book where a girls brother has heart problems so she goes to live with her grandma

so in this book there is a girl and her brother has heart problems and he's in the hospital and her parents are stressed so the girl goes to live with her grandma I think on her dad's side. her grandma lives in the middle of nowhere in a small section of the woods. people want to tear down the woods bc the trees are too close to the house and it's unsafe. the girl lives there all summer and goes to summer school, the girl goes into the woods to get to school and through a field. one day walking through the woods she meets a girl in a red hood/cape or maybe red boots. and they become friends. the girl talks about fairies and something about a fairy circle made of mushrooms. one time they look through a hole in the tree and they see fairies. um, I think there is a part where her grandma tells a story where some boy dies climbing that tree, I think it's the girl's dad's brother. the girl finds these letters in a room she's not supposed to be in and they are letters from someone's brother I think. um, somewhere at the end the girl's friend from back home comes over I don't know why, and the girl tries to introduce the two her two friends, but the girl with the red something is gone and she realizes she isn't real maybe... I think the girl with red something her name might be Alice...

In Darkling Wood by Emma Carroll?