Welcome to Just Answer!
I would like to help you and your dog with this question, but need a bit more information in order to better assist you.
You are absolutely right that grapes (and raisins) are toxic to dogs.
The dose at which we may see raisins causing kidney failure is as low as 0.11 oz of grapes per kg of dog. So, in your 16lb dog, that would be about 2 oz ounces of grapes.
Is that how much your dog may have eaten?
Symptoms of toxicity start in 2 to 8 hours: vomiting, diarrhea, abdominal pain and/or lethargy.
I will also include some links to further information on this topic:
If you think that there could have been close to 2oz of raisins in the mixture, then it would be prudent to induce vomiting. If it was less than this amount (say, only a teaspoon or so of raisins) then you don't need to worry.
I am happy to tell you how to induce vomiting... but do always check with a vet before doing so. There are some situations in which you should NOT induce vomiting (such as if he ate something sharp like a bone, or something like used engine oil, or a battery if it was punctured and the caustic material was leaking out.. these things are better dealt with in the stomach as it is stronger than the espophagus which could be damaged during vomiting these things). To make her vomit, you could take your dog to a veterinarian immediately as this is the safest possible option. If this is absolutely impossible, you could attempt it at home, but know that there is some small risk of aspiration of vomitus. You can make your dog vomit by using 3% hydrogen peroxide. Give 2 teaspoons per 10lbs body weight. If your dog weighs 16lbs, then you could give 3 teaspoons which is 1 tablespoon.
There are 2 ways to do this: 1. METHOD ONE Tip her nose to the ceiling and pour it down her throat with a shot glass, or a turkey baster. To do this, hold the dog between your knees with you kneeling on the floor. Have the dog face away from you. Point the nose to the ceiling, open the mouth and quickly pour the FULL dose into the back of the mouth. You can repeat in 10 minutes if she has not vomited yet. More here: http://www.petplace.com/dogs/how-to-induce-vomiting-emesis-in-dogs/page1.aspx I find the shot glass method to be the most effective! 2. METHOD TWO If you are not able to give it by mouth as described above, you can use the following method: 1. Feed a small meal or slice of bread first - they are more likely to vomit with some food in the stomach. 2. Dogs will often drink peroxide if you mix it 50:50 with milk or ice cream, and it is just as effective. 3. Dogs are more likely to vomit after getting hydrogen peroxide if they move around - play ball, go for a walk, run up and down stairs - as this heightens the fizzing. 4. Always check the expiration date of the peroxide. If it is old it doesn't fizz very well! You can repeat in 10 minutes if she has not vomited yet. You should not do it more than twice. The vast majority of dogs will vomit with this! It is useful in case she eats chocolate, prescription medications, or sugarless gum containing xylitol. Hope that helps!
If your dog does develop vomiting, diarrhea or abdominal pain then I would certainly contact a veterinarian promptly.
If this has been helpful, please accept my answer and leave feedback. If you have more questions, just click on reply and I will still be here to provide more information.
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.