I responded to this but apparently it didn’t post, so I’ll try to rewrite what I said. haha

I don’t mind at all if you run what you want to say by me first. If I were you, I’d probably not go into too much detail with what you say though. I wouldn’t mention your ex at all and make it more about how you feel you aren’t romantically compatible and that you two just aren’t a match for each other.  Those are pretty concrete things that aren’t anyone’s fault but also can’t really changed. You’re either right for each other or you’re not. Keep it simple and then honestly answer any questions she has.