Need to find out if the ex has been saying things or where this is coming from. SOMETHING obviously has changed. I've been in a similar situation for the past SEVEN, even though I'm not dating this guy and never have, he's been a friend for almost 20 years. He and his daughter lived with me for almost three years. I've been a part of her life since she was an infant (he and the mother were engaged but never married - THANK GOD).
What I realize when this kind of thing come out of her mouth, mother has been talking and she ends up admitting what her mother had said. We then talk about the reality of the situation. Many times, at 7, she's able to figure it out herself when we talk about it. I try and ask her questions to help her think things thru and let HER answer he own ?s. That way, I'm not putting words in her mouth -- RATHER......actions speak louder than words. REPEATEDLY, the past year, she's said, "I wish my mom would quit lying."
Unfortunately, she's learned some of her mother's manipulative habits, but we're on top of it.
Also, there is a book called RAISING RESPECTFUL CHILDREN That you might want to look into. This might help. Respect is something that is LEARNED, it's not automatic. We live in a society that doesn't seem to know much of that at all any more. Good luck