Great. Thanks for the additional information. I really appreciate it.
The toxicity of chocolate is judged by the amount of theobromine in it. Milk chocolate (like the kind in candy bars), contains 60 mg per ounce of theobromine. The toxic dose is one ounce of milk chocolate per pound of body weight. For example one pound of milk chocolate is poisonous to the nervous system of a 20-pound dog. If you figure it all out, it ends up being that it takes 2-3 chocolate bars to be toxic to a 10 pound dog.
Since she ate it several hours ago, the only thing we can do is to adopt a watch and wait posture. The symptoms of chocolate toxicity include trembling, nervousness, shaking, increased heart rate, panting, and worse case scenario, seizures or death. Dogs that eat dark baker's chocolate squares are at most risk of seizing or dying from chocolate. I would also keep an eye open for tense stomach, attempting to vomit or defecate with no success and abdominal swelling as this can be a sign of intestinal blockage from any leftover wrappers that she may have ingested.
If you notice any symptoms, then you should have her seen by an emergency vet tonight...that being said...even if you make it to morning with no symptoms, you should at least give your vet a call and see if they want to do any blood work...just to be on the safe side.
I hope this helps.