DO NOT breed a dog unless it's been health tested, you know the lineage of the dogs and therefore know potential risks etc, and you know what you're doing. There are tons of homeless purebred shih tzus in shelters right now. Why add to the problem? How did she 'accidentally' get pregnant? If she was in heat you should've been responsible and been watching her and definitely shouldn't have let her around a male dog unsupervised. IMO you should just have your female spayed.