I had a look at a clip that shows the difference between a heart-related cough and kennel cough and I'm glad to say her cough seems more like the latter.
It's not a bad cough, so we're not going to the vet yet, but if it's worse tomorrow we'll get her checked. In the meantime, we're going for only short strolls, aiming to stay away from other dogs in case Penny's contagious, and also to let her rest and recover.
I'm trying a remedy suggested to us by a tradesman who was here today, and who is a dog lover. (BTW, we do wonder whether the cough is a result of months of home renovations and the consequent dust.)
After he suggested honey and vinegar, I looked at America's Blue Lacy Dog Blog, which has an article on natural remedies for kennel cough. We're giving Penny a little bit of - super expensive! - Manuka honey and putting a touch of apple cider vinegar in her water. The woman in the health food shop said the vinegar is better than most, because it has 'the mother' in the bottom of the bottle.
A site called Authority Nutrition (now there's an impressive title for a site, lol) says:
Organic, unfiltered apple cider vinegar...also contains "mother,", strands of proteins, enzymes and friendly bacteria that give the product a murky, cobweb-like appearance.On reading more, I gather that there's some thought that we shouldn't give too much honey to dogs, so I guess we'll only try it for a couple of days, and assess her stools and her general health. After all, it's wonderful stuff for humans, so it won't go to waste.
There's a great deal of information about honey and about its benefits and dangers for dogs here.