My roommate's dog ate (I think) a Kind bar and a chocolate-dipped biscotti. She's a cattle dog/pit mix, about 60-65 lbs.

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Was the Kind Bar coated with milk chocolate rather than dark chocolate?

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I am sorry to hear about Zoe's problem, I know that you must be very concerned. Hopefully, we can get this resolved quickly for you.
Good news, I very much doubt if this incident is going to adversely affect Zoe very much, in fact, there are no special measures you need to take other than just keeping an eye on things. While chocolate can be toxic to dogs under certain circumstances they have to eat quite a lot, probably very much more than Zoe ate today before you would see any signs of toxicity. But let's talk things over in more depth ...
You see the rule of thumb which I apply is that with dark chocolate { Which is way more toxic than milk chocolate } mild signs of toxicity can occur when 0.3 ounces per pound of the dog's weight body is ingested. Severe signs occur when 1 ounce per pound of bodyweight is swallowed. If you estimate Zoe's weight as being in the region of 60 pounds then you can see that your roommate's dog would have to swallow 18 ounces { More than one pound! } of pure dark chocolate before any symptoms would even start to occur.

Clearly, the amount of chocolate involved today is going to be very minimal by comparison, so no worries as far as chocolate toxicity goes. And the other ingredients both the Kind Bar and biscotti are likely to be non-toxic to dogs.
That said some dogs might perhaps suffer a mild transient bout of vomiting and/or diarrhea, this can happen when a dog suddenly eats any sort of unaccustomed rich human food. However, should this occur it is likely to be very minor and in any case, it should soon pass on its own.
I am telling you the following just for your information as Zoe ate so little you do need to do anything and need not be too concerned.
The symptoms of chocolate poisoning would include vomiting and diarrhea as well as frequent urination, and restlessness in the early stages. This can then progress to cardiac dysfunction, tremors, and fits. Of course, you should call your vet without delay if any symptoms appear.
Having said that most dogs with chocolate poisoning will recover within 24 to 48 hours, particularly if serious symptoms do not occur. There is no specific treatment for chocolate poisoning only symptomatic treatment.
Here is a link to a very accurate article on chocolate toxicity in the dog, follow this to check the accuracy of my advice and read more on the subject: https://www.petplace.com/article/dogs/pet-health/chocolate-toxicity-in-dogs/
But in any case, I should be available online for you for the next four or five hours today so please do not hesitate to get straight back to me in the very unlikely event that Zoe's condition changes in any way or you would like to talk things over with me further.
Regards,
Dr. Scott
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No problem, I am very glad to be advising you.

Kindest regards,

Dr. Scott

Hello again,
I am just checking back in to see how Zoe is getting on?
Regards,
Dr. Scott

Thank you for visiting JustAnswer, I hope you are happy with our service. But please let me know if you still need me to clarify anything or if you have any additional questions related to your current issue - I am always happy to help.
Kindest regards,
Dr. Scott

Thanks so much for the update, I am so glad that Zoe came through this OK.

Kindest regards,

Dr. Scott