Another way is to simply look at your bitches, when they're in heat, during the schooling process. It won't take long, and it's not anything serious. The main objective is to determine how your bitch performs during being in heat.

As for the aforementioned female, I couldn't really say without knowing the dog and other things. It could be the owner's fault OR it could be the females. I've never owned a dog that changed what she was, performance wise, due to having pups. I don't really think I've ever seen that from anyone else's females that I'm familiar with. That seems odd in of itself, in my experience, and that alone would make me question the female and my judgement.

We, as owners, have the responsibility to make sure the dogs are up to the task before we put them in those situations. Take the time to do the small things to make sure all is well when it comes time for the big thing.