This sounds so mysterious and interesting

I really love books like this. I enjoyed the switch in narrative between present day and the past when whatever they did happened. I like the realistic change in the main characters as well. She's harsher and older in the present day chapters but more curious and girly in the past chapters. Female friendship focussed books are always interesting and complex. I'd be excited to see what happens and what happened then to result in the main character behaving the way she is.