Hi Kate (from Kate!)
Unfortunately, CM/SM is a progressive chronic disease and with a marked malformation so young, Rosie is likely to develop a syrinx at some point in the future. It is really heartbreaking for you having to face this with such a young dog. Chiari Malformation on its own can cause pain, even without a syrinx, which is why I imagine Rosie has been put on gabapentin. Fortunately, gabapentin is a drug with very few side effects (initial drowsiness is one symptom, but that wears off after a week or two), and it mixes well with other drugs. It can become ineffective with some dogs as their CM/SM progresses, but there is a refined version of gabapentin called progabalin (Lyrica) which can then be used to good effect. Sadly, symptoms can be controlled, often effectively, but they will not be eradicated. One avenue that I am sure your vet/neurologist will explore as Rosie gets older is decompression surgery at the back of the skull. So there are options for treatment, and I hope her present dose of gabapentin is helping Rosie to enjoy being a puppy, and you to enjoy owning her, in spite of your worries.
There are many people on this forum with experience of CM/SM, so please don't hesitate to ask questions!
:hug:
Kate and Ruby the Blenheim rescue