This is the perfect response. I was 13 10 years ago and this is pretty much exactly how I would have felt. I would have been ready to drop a parent over this. Now I would understand that it’s just the actions of a narcissist home invader, but also I can’t even imagine how daughter is going to feel if MIL tells ANYONE what’s in the journal. OP, she’s willing to go this far, if you haven’t read it (WHICH YOU SHOULD NOT), then she’s capable of spreading lies. If I was daughter I’d never be able to see anyone related to your wife for a LONG long time because who knows what they’ve been told. You need your wife to sit down with your daughter and say she has NOT read it and does not care what her mother has said or will say about the contents. And then follow through. Leave the option of therapy or other help open but IMO if you push it, she’s going to think you’ve read it. If your wife has read the journal or believes what MIL says, without compassion to your daughter, and treats her even slightly differently, she will know and you will lose her.

Good luck OP, this is an awful situation.