I would spay and place both of them as I feel this is not normal lab behavior!!

All my dogs live together and at times I have had up to 8 breeding males running together. Not a growl to be heard. I have even bred a male and turned him out with the rest right after the breeding. Everyone (males and females) give him a good smell and then off they go.

When I have a litter, all my dogs and my cat help with the puppies. We are a family and all live together as such.
My labs are known for their great behavior and are used as working dogs in all venues.

I have also spayed a CH BOB bitch that produced one litter with champions in it and gave her to a single dog pet home. She growled and then went after another bitch. That was enough for me.

I was not going to live in fear and I was not going to set up kennels to keep dogs apart. I have labs just for that reason.

How hard is it to place a dog like this?

Usually not hard at all - haven't ever had to place a girl like this, but have had one girl who didn't like another - both were great with every other dog, it was just those two girls' dynamics. I just made sure I was there or they were not out in the yard together when I was gone. Typically, this behavior is very specific to the one girl they have an "argument" with. If it goes beyond one, then there's some serious thinking to be done as far as the lines you are breeding!

I would think it would be difficult. Won't the new owners want to know why your placing the dog? Question is, when placed how do you know the dog won't go after another dog.

If you have any number of dogs and have taken your dogs out to shows and among other dogs, it's pretty easy to know that the dog is reliable with every other girl but that ONE they have chosen as an arch enemy. If you haven't seen this phenomenon, then you haven't been in dogs for long. There is a reason the word "bitch" has a negative connotation in the English language!

Then again, bottom line - you can NEVER be 100% sure any dog won't snap - they are animals and while I would be shocked if any of my dogs went after another dog, I won't say it couldn't happen given the right (wrong) set of circumstances!

I've had Labs for almost 40 years and multiple girls in my kennel over 30 years, and I've never had two that I had to keep separated when I was not with them- ever! Likewise for the boys, even when girls are in season. I do have two girls that play so roughly when I first let them out for their evening walk that I keep one on leash for the first minute or two until the excitement ebbs. I can turn them out into the airing yard (not as exciting as the daily walk) and they are fine together -best friends - no wrestling.

How would you deal with it?

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.