@Smilada I've only tried mating dogs who both lived in my sims' household so I've never experienced your issue.
If I were you, however, I'd try three things:
* Choose a male dog with traits similar to your dog;
* Make sure that the two dogs have a good relationship. Have them interact and check that they're throwing off green ++ icons;
* If all else fails, you could enter Manage Worlds to temporarily move a male dog with compatible traits into your sim's home.
This makes things a bit easier since you could direct both dogs to "Be nice to..." each other.
Once you're sure that your female dog is pregnant, you could then return to Manage Worlds and either create a new household for the male or move him in with a neighoring household.
Good luck!