The dog’s not well. And having a sick animal is a proper pain in the particulars, for various reasons.
The first thing is that when she’s floppy and listless and won’t eat and you don’t know what’s wrong, and, you know, she’s quite old… well, it’s something you can do without. Secondly, when the vet reassures you that she’s not dying and then the treatment begins, you have to administer medicine and change dressings. It’s you she’s always trusted never to harm her, but it hurts sometimes and she just wants to be left alone. You can see in her eyes that she doesn’t understand, and you can’t explain. That. That’s the worst part, probably.
Also, you have to stay by her side and nurse her, 24/7, for a while. Which, when you think about it, isn’t such a bad thing.