Hello! My name is XXXXX XXXXX it will be my pleasure to help you with your dog today.
I'm sorry to hear that your dog is feeling so poorly. It's always tough when dogs get to be elderly..so much can be affecting them, and yet they have no way to tell us what is going on with them. When you add to it the fact that Daisy has a pre-existing neck injury, and it makes it even more concerning.
The 'knuckling over' that you describe sounds more like a neurological (nerve) problem than a leg injury. Older dogs tend to get communication problems between the limbs and the brain. This happens because the nerves in the spinal canal can be injured or simply decide that they're done working..so they don't transmit the proper signals to keep the paws in the normal position they're supposed to be. Since she did hurt her neck last year, it's not hard to imagine that the injury has gotten more involved, and could be pinching nerves or impinging on tendons, causing her to limp and drag that paw.
If Daisy were my girl, I don't think I'd wait for that next appointment to take her back to her regular vet...I'd call them today and request that they take a radiograph of her spine...perhaps there is a disc protruding and impinging on the spinal column or something like arthritis causing this limping...that could be a possible cause of the 'miscommunication' in the nerves.
If that all comes back negative, it might be time to ask for a referral to a veterinary neurologist. Not only will they be able to figure out what is causing the leg weakness in her limbs and will be able to get her on medication that may take care of the pain more than her current medication plan of Deramaxx.
I hope this helps