My pregnant dog has ringworm. What's a safe treatment option?

First of all it is necessary that you have a definitive diagnosis that your dog is indeed suffering from ringworm, so you do not give her medications on suspicion of ringworm. There are quite a few diseases that can look like ringworm, especially bacterial infections.
So if your dog is indeed suffering from ringworm your vet will prescribe either a topical treatment (depends on the extent of the ringworm infection) such as an antifungal ointment, or a antifungal bath, and/or also oral medications. Both Itraconazole and Ketoconazole tablets have pregnancy risks, so possibly would not be a good choice to treat ringworm during pregnancy whereas a topical shampoo containing a fungicide may be a suitable choice. I suggest you see your veterinarian with your dog for a proper diagnosis and his recommendation for treatment as he will know best after examining your dog.