The vet suggested I might have seen Penny reverse sneezing, or that perhaps her sneezing relates to allergies, both of which suggestions sound sensible to me.
I have seen Penny reverse sneeze, and PetPlace has a couple of video clips of dogs reverse sneezing. I'll keep an eye on her and check whether that is the issue. If it is, I won'tworry, as reverse sneezing doesn't seem to be a big problem.
One symptom was that when she barked, she would start sneezing and coughing, but seeing she's at the front door right now, barking up a storm to tell us there are cats in the front yard, I guess that's not a problem now.
As soon as we arrived at the vet's this afternoon, Penny looked the picture of health - as usual. I guess vets get used to owners saying, 'But she looked sick when we were at home!'
On the way home, we called in at Bundoora Park.

There's a little hill - called Mount Cooper, because our continent is so flat that we call every anthill a mountain - and we had a great view from there. It's an old volcanic vent, but seeing it hasn't erupted for 9.2 million years, I felt safe.