Hi there. My name is ***** ***** I'm happy to help you with your question today.
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.
Obviously, she didn't get anywhere near that amount even if she ate the whole pan of brownies.
Of course, it is always better to be safe than sorry, and the safest thing to do is to induce vomiting in your pup. Details on how to make that happen can be found here: http://www.petplace.com/dogs/how-to-induce-vomiting-emesis-in-dogs/page1.aspx
The best thing to do is give her some peroxide. Then 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. I don't expect you to see any of these issues, but it's good to be aware of the symptoms, just to be on the safe side.
Even if you're unable to get her to vomit, I still woudln't be too worried about it. Just keep an eye on her.
I hope this helps.