> After 2 weeks I would be asking the vet to have a look at that pad.
Good point. A friend had a similar experience with her dog. It proved to be an abcess that had formed inside the pad. They didn't know how it happened but the vet guessed that it might be due to friction, or a cut that had healed with some kind of infection inside, perhaps due to a bit of grit. Her dog had to be anaesthetised, pad cleaned out, stitches, antibiotics and a Comfy Collar for a week.
Hope all goes well with your bitch Arnie.