So, you don't actually know the amount or the needle gauge? Although, I believe an insulin needle is typically 25 gauge, but the syringes themselves come in all different sizes, and most of them have orange caps. I would suspect a too large of a dose might be uncomfortable.It was just a bit less than half of an insulin syringe (orange cap). I chose this syringe because it's the smallest and thinnest gauge I could find. She doesn't react to the needle but to the B12 - which I've at times myself also experienced it as somewhat uncomfortable.
It's not refrigerated. Could be she is just sensitive. IDK.That sounds better! But still might be a bit too much. I don't know if that would cause the discomfort you say she is experiencing.
I presume you are not refrigerating the fluid? If so, you don't need to and maybe that would help with alleviating any discomfort. The only other thing I would suggest is going back to the vet and ask them to do the injection in front of you and see how she reacts when they are doing it. If they notice it is uncomfortable for her, perhaps they would be willing for you to try giving her an oral B-12 supplement instead.