The dialogue referenced above is in the movie. Another Fredo-Deanna confrontation was deleted:
https://youtu.be/MkVdDZozUKcDeanna Mystery! why did she marry Fredo
I don't think we know much about Deanna. There's a Deanna in the novel, but this doesn't seem like her. She seems more like Johnny's second wife. Failed starlet? Aging call girl?
How did Deanna know who Rocco was / his name?!
She should know him - he was in the family before she was.
