Hi and welcome.
So sorry you have had this diagnosis. :flwr:
As others have said there are many here with SM dogs (I have two of my five, probably three but one has not been scanned). Dogs can be affected in many ways. Many will never show symptoms or obvious symptoms, some never progress (though this seems to be uncommon...), some progress very slowly, some progress quickly. Some will have their best chance with the decompression surgery; others might do fine on medications though medications do have a lower rate of success with more dogs needing to be PTS earlier. Much depends on the individual dog, and treatment is a highly personal choice for the owner with many different factors influencing their choice. There is no right answer -- though I think it is also important not to neglect all the current research evidence which does indicate most dogs will progress, most dogs on meds will need regular adjustment of medications to manage pain especially if they are being treated medically alone. Some -- like me -- prefer to wait on surgery in the hope that their dog will reach a 'normal' lifespan managed on meds, but there is good evidence that early surgical intervention does have a better result as opposed to waiting while greater neurological damage is done.
The earlier the diagnosis the worse it tends to be. (although not definate or proven I beleive)
To adjust this slightly -- it is actually the earlier the onset of symptoms which may or may not be tied to diagnosis -- some people with badly affected dogs only realise years later that their dog was symptomatic but incorrectly diagnosed. Dogs with symptoms/diagnosed before age 4 are considered 'early onset', and younger than 2.5 are considered to have probably more severe SM in most cases than dogs that don't show symptoms til much later. This is actually 'proven' to some extent (through several studies now inasmuch as it can be, and I am aware of a further study, quite large, which further confirms this) . However dogs do adjust to the level of pain with this horrible condition so owners and vets can easily miss symptoms and then think the dog has gotten 'better' on its own when it has just learned to tolerate the new threshold for pain. Also medications do not halt progression but simply relieve the pain/discomfort (there is some but not definite evidence that a CSF inhibitor can in some cases slow or halt progression but this is by no means definite and not for all dogs). That means medications can mislead owners into thinking their dog is 'getting better' when more likely, the condition is progressing but the symptoms are masked.
So there's a lot to weigh up and a lot to consider.
I agree that it is a good idea to have dog on a CSF inhibitor along with pain meds. Many people find they see a reduction in pain with the CSF inhibitor.
As noted pregabalin is expensive. However some neurologists feel it handles pain better for many SM dogs than gabapentin. It also remains longer in the system so doesn't need to be given as often. Unless a dog is in a lot of pain most neurologists would start with gabapentin.
What is very important is to keep an eye on how your dog is managing on her medications and be sure to return to the neurologist or work with your vet (who is presumably, speaking to your neurologist) on the medications mix. Most neurologists do feel medications work best in combination and need regular review.
On a personal note -- I have a 7 year old with a wide syrinx (these tend to be far worse for pain than longer narrower syrinxes, and lopsided syrinxes are also worse than evenly centered syrinxes). He has been on meds for 5 years now and has only had one serious pain session which in retrospect was probably precipitated by a fall and the kind of changeable weather that tends to make these dogs more uncomfortable (probably due to pressure changes). I have a 4-5 year old with a very small syrinx but very large ventricles who has some scratching and little else. The undiagnosed dog has persistent mild scratching at 7. The other 7 year old with a wide syrinx now has a moderate grade heart murmur (the other horrible and endemic condition in this unfortunate breed) -- so now I am always weighing whether he is of the age where surgery would ever be worth doing as his heart might end up the larger problem. Management is a persistent worry with these dogs and you are always having to weigh up doing A against doing B.