I'm sorry to hear that Cha Chi ingested some milk chocolate while you were out. Chocolate can be toxic, but they do need to eat a certain amount per pound of body weight in order to get sick.
A 43 pound pup would need to eat 6.1 ounces of milk chocolate to see symptoms of drooling, nausea, vomiting and diarrhea and almost 12 ounces of milk chocolate to see hyper-excitability and an elevated heart rate.
At higher amounts we can see muscle tremors and possible seizures.
Since she ate the chocolate 3 hours ago it is too late to make her vomit, and given the amount she ate (which shouldn't be enough to cause signs of toxicity), I don't think you need to do so anyway.
At this point I recommend that you just watch her for now.
I would encourage you to get her to drink as much as possible and to get her out to urinate frequently. Chocolate toxins are metabolized out through the kidneys and can be reabsorbed from the bladder so we don't want them to sit in her bladder .
In most cases mild chocolate toxicity is out of their system in 24 to 48 hours. We generally begin to see symptoms, if they eat a toxic amount, within 4 to 6 hours.
It may help to with-hold food next 12 hours to stop intestinal spasms which can lead to diarrhea.
If she seems at all nauseous to try and settle Motley's stomach you can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of one half of a 20mg tablet per 20 to 40 pounds of body weight every 24 hours
These are acid reducers and should help her feel less nauseous. They are quite safe and can be used days if needed.
Then after her 12 hours food fast to decrease the symptoms of stomach upset you can feed her a bland diet next couple of days. A homemade bland diet is a mix of 1/3 boiled, minced, white, skinless chicken or lean, boiled hamburger and 2/3 boiled, plain, white rice mixed with some low salt chicken or beef broth to make it easy to lap up and swallow. Feed small meals frequently.
If you do notice a very rapid heart rate (more than 160 beats per minute in a small dog) repetitive tremors or seizures then she should be seen by a veterinarian on an emergency basis . They can use injectable medications to control her heart rate and stop the seizures until the toxic levels fall.
Given the amount that she ingested I highly doubt that you will see any symptoms. If she tends to have a sensitive stomach you may see mild nausea or loose stools, but that should be all.
Best of luck with Cha Chi, let me know if you have any further questions.