Yet my SO is. No idea why, but she's really scared of them, especially dogs she doesn't know. Even a chihuahua is terrifying.

Dogs can attack with no indication or reason, some breeds take more of a lion's share for that than others. It is entirely reasonable to feel fear in the presence of a dog, especially if you've been the victim of an attack or seen one before. The conversation around responsible dog ownership is really delusional.