Welcome! Thanks for asking your question. My name is***** am a licensed veterinarian and I will be assisting you today. Friend, chocolate toxicity and symptoms are very dose dependent. Symptoms can range from gastrointestinal symptoms to life threatening seizures
or cardiac arrhythmias. It is not likely that two bites of a flat brownie cookie will be toxic
to a 15 lbs dog. But, to be on the safe side you can try to induce vomiting with hydrogen peroxide 3%. This is what you can do:1- To induce vomiting give her 1.5 (one and half) teaspoon of hydrogen peroxide orally. 2- Allow her to walk for a minute and move her belly to mix stomach
content with peroxide. If she does not vomit within 5-10 minutes, repeat it again. Can give a total of 3 times 5-10 minutes apart.3- If she does not vomit after 3rd dose or you do not see the chocolate in the vomit observe her for the next 24 hours. If she becomes hyperactive, muscle
tremors, changes in respiration, etc. have her checked immediately by ER veterinarian, these are symptoms that could progress to life threatening seizures or cardiac arrhythmias. If no symptoms after 24 hours (especially the first 12 hours) she will be fine. My goal is to provide you with excellent service - I hope I've provided the information you were seeking, if you feel you have received anything less, please reply back as I am happy to address follow-up questions. Kindly rate me when you are done.