It is written by Christian psychologists from a Biblical perspective. It helped me a great deal when dealing with a difficult situation with my mom and I am a lot older than you. Family situations can indeed be difficult, even when we are all believers!
Try to love her and honor her, but use the tools taught by the book. You may even want to speak to a Christian counselor or pastor.
And certainly, pray about the situation as much as possible. I wish you the best! Blessings!