Is it still nursing off of mom too?Have you been weighing the pup every day to ensure she's not losing weight?Have they had their first vet check yet?
Has that puppy only been throwing up today?How many times have you fed them the Iams?
Thanks for answering my questions.
The puppy could be having some digestive upset from adding the dog food into her diet, so I think it it were me, I'd skip giving her any more dog kibble tonight and just allow her to nurse instead. If you don't think she's eating at all, then you can try rubbing a little Karo or pancake syrup on her gums just to keep her form becoming hypoglycemic (low blood sugar).
If she's still acting sick tomorrow, then you absolutely, positively need to have her seen by her regular vet. I understand that finances are an issue, but if she continues to be sick tonight, then you should have her seen by an emergency vet, just to be on the safe side.
I understand that you(like so many other people) are in a hard financial spot right now. There are some organizations that might be able to help. If you'll follow this link: http://www.speakingforspot.com/helppayingforveterinarycare.html , you'll find dozens and dozens of organizations that may be able to help pay for you to take your dog to the vet. Also, there are some clinics who offer free exams and other treatments and require that you only pay for medications. If you'll follow this link: http://www.vcahospitals.com/main/offer , you can see if there is one in your area.
I hope this helps.