We do see less adverse side effects when the dose is started low, so with Sydney's weight of 17.4 lbs I believe starting her dose of Vetoryl at 10mg is a good plan.
Some dogs may get an upset tummy from the Vetoryl but this is usually because the dose is too high. If Sydney acts like her tummy is upset than I would ask her vet about giving her pepcid ac before her Vetoryl dose.
We are here for you and do understand how scary this can be, however I believe you and Sydney will do just fine. If you have any questions at all please do not hesitate to ask them, ok?
Hugs, Lori