How often should I wash my doggy?

Hy guys real quick question. I have a pomaranian and chihuahua mix. I dont wanna wash her too often because my aunt washed her terrier every week and her dog get a skin infection. So I think i wanna bathe her once every month. But if lets say it was really rainy and she got wet and dirty is it okay if i just bathe her with clean water and no soap as often as I want? I know seems like a dumb question but I have no common sense sorry and ty guys <333