Oh sorry, I read that as her being three.
On the scratching -- this can be managed in many ways and does remain a sign of discomfort -- most neurologists do not consider it something that should really be left. At 7, she is unlikely to build a resistance to gabapentin -- many, maybe most dogs need more over time not because they build a resistance but because the condition progress. As well, there are many other drugs that can manage scratching -- Lyrica (pregabalin) being a generally more effective form of gabapentin, for example; many dogs here are on it and find it works when gabapentin doesn;t. Also: the dose needed to manage scratching has to be determined for each individual dog and reassesed. Some are on 100mg three times a day, some are on 300mg 3x for the same result. It may not have worked because the dose was too low/the trial too short.
She may actually also need a daily pain medicine like Metacam (which I use for Leo on his bad days, but many dogs are on troxocil or other meds). These can be used alone but generally are used with gabapentin for scratching dogs. If she is continuing to scratch, and is also having sessions where she is confused, I would really stress how imortant it is for her neurologist to see her and assess these issues. The scratching can be helped (meaning the underlying pain/discomfort can be helped) and it would be im[ortant to assess if the confusion is related or not and if it implies further pressure in her cerebellum etc. A vet is just not adequate to assess these issues -- it would be like seeing a GP to manage a cancer diagnosis or a brain tumour (or SM for that matter). The continued scratching and the confusion could indicate a decline post surgery as well that should be assessed, perhaps whether she has developed scar tissue or the condition is progressing for other reasons. And hydrocephalus -- which would cause confusion -- is a consideration in undersized dogs (it is a reason sometimes for them being small, amongst other possible health reasons) as well as being seen frequently in SM dogs, and a neurologist can assess for that.
The panting could be from MVD, but can also be a sign of pain. If she has seen a vet annually it would be odd for no murmur to have been picked up well in advance of her starting to pant heavily, which is usually a sign of more advanced MVD. They can have very rapid onset but usually you would have picked up a murmur at least a year or more before seeing panting associated with MVD.
Either way I'd see both a vet and a neurologist for the other issues. She should not be be 'special' after this surgery -- it is an indication that something is not quite right and a neurologist needs to assess what might be going on. Dogs do internalise pain -- as is mentioned in another thread, there's a new research project starting to try and assess pain in SM dogs because much of it is internal extreme headache and other signs that may not be visible to owners or vets (or neurologists). Humans report severe pain of this sort but they can speak, whereas our dogs cannot tell us what is going on. I know you would not want her to be suffering -- that's why it is so important to have a neurologist assess her especially if it has been four years since her surgery and she is still scratching.
If your vet diagnoses a murmur then it's a good idea to see a cardiologist as vets are mediocre at getting murmur grades correctly and so-so at treatment (eg they take a quite standard approach that often introduces meds too early or too late or the wrong ones).
Some others who have dealt with both surgery and MVD might have some other ideas or observations.