How can fatten up my picky Chi?

My Chihuahua is 3 years old and just had her first litter on the 19th of April. I had to take her to the vet today because I was getting very worried about how skinny she is getting. Also, for the last 2 days her pups are not gaining the weight they should be. The vet said that she is definately under weight and that because of that, her pups are not getting enough milk. I told her that because my Chi has a very severe underbite, she has a very hard time eating dry dog food. I have always given her wet food. The vet gave me some suggestions on what to feed her but after a whole day of shopping, I can't find anything in a wet food. Does anyone know of a high quality PUPPY FOOD that is wet? Or any other ideas on what I can give her that will be good for the pups too? Thanks so much everyone!