Oh! That may explain something - my 16-week-old girl, Willow, has been really good with all dogs, even on leash. Today we ran into this Shih Tzu who was nonstop barking in her face. After about 30 seconds, she snapped at him. Again, this is only the second time - first growl was a couple weeks ago at a barking ****er. All other encounters with dogs and people have been great, even when she is approached on-leash.
I can't say I blame her - that dog (and owner) is annoying. Unless anyone has specific concerns about this behavior, I think I'll keep her away from barkers. Any other suggestions? I'm definitely getting Control Unleashed.