Thank you for your question regarding your girl who has managed to ingest a 1.5 ounce dark chocolate bar. Good on you for acting fast and trying your girl with hydrogen peroxide. This method doesn't always work unfortunately, and now that you have done it twice, it is best not to attempt it again. If it has been 20 minutes after the second attempt, then you could have one more go with 1 teaspoon, following the full tips given online here: http://www.petplace.com/dogs/how-to-induce-vomiting-emesis-in-dogs/page1.aspx
If that is also unsuccessful, then I would recommend a trip to your local ER vet so they can give your girl some apomorphine. As your girl is quite small and she managed to eat dark chocolate, the amount here would be enough to cause moderate symptoms here that could potentially include fast or irregular heart rate, tremors, seizures, increase thirst and extreme hyperactivity. As such getting her to vomit this up would help to remove the chance of these potentially nasty side effects of chocolate toxicity.
If you do try one more time with a teaspoon of hydrogen peroxide and this works to cause her to vomit all of this chocolate up, then there shouldn't then be a concern. If there is no luck again however, then definitely get her seen. I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask!
PS: If you have additional questions after you rate the question, you are welcome to request me for additional conversations if I am on-line or by beginning your question "Dr. E..." or "Pet-doc..." and others will leave the questions for me.