Had a Ch bitch with all clearances. She was a definite improvement over her mother in many ways except temperament.

She did not like other dogs! At all. Same sort of thing - started with the occasional growl and moved up to full out attack mode in a matter of weeks. She was good with our pack, it was dogs met while out walking, at shows etc. Her's is an insecurity issue - tried working through it, put obedience titles on her, etc. She was well socialized from a young age with people and other animals.

I did place her with full disclosure to anyone who inquired about her "intolerance" of other dogs. Loves people and cats, is a dream to work with in obedience and at the Vet etc. She lives with a wonderful couple who have two cats, live at the end of a dead end road and have no plans to add another dog ever. They love her to death and she boards with us up to 12 weeks each year as they love to travel. She grumbles at the dogs that might be new to our pack between our visits, but a reminder from me that it's not an appropriate manner and she's fine. But, for me it wasn't the Labrador temperament that is my goal for breeding.

So in all my recommendation for your question on how to approach her behavior when talking to prospective new owners is full disclosure.