Baby Shampoo For Puppy?

[Nanemy]

You were all so helpful when we randomly got a puppy last March so I thought you might be helpful again. We haven't washed our puppy for oh goodness at least 3 months now. How often should I wash a dog? She's an outside dog so I don't have to smell her - lol. Should I just make it a once a month habit? And what soap do you recommend? I was planning on washing her today, even though it's raining, do you think it would be OK to use Johnson baby shampoo just today and then I can get a special soap for next time? Not entirely sure but she should be about 9 months old now if that makes a difference.
Thank you!!