How can I add calories to my dog's no fat diet?

Several years ago my small dog(a small feist) was diagnosed with intestinal issues due to her fat intake.I had been feeding her store bought brand name food and I didn't know why she was throwing up and had diarrhea.A local vet specialist put her on a no fat food in a can(it is very expensive).Only 1 to 1 1/3 can a day.I have stuck to this feeding regimen ever since the diagnosis.However she has lost a lot of weight and has become very,very thin.Is there a way I can add calories to her diet without putting her back on store bought food?I did try a very well known food that can be bought in stores and at the vet's office.It did not work,after several weeks she started with the same sysmptoms before the vet put her on the no fat diet.I DON'T feed her table food AT ALL.***PLEASE,IF THERE ARE ANY VETERINARIANS OUT THERE THAT CAN GIVE ME SOME ADVICE,PLEASE HELP ME?*** I have had her for about 14 years and she has been well taken care of ,lives in my home,pampered.Thank you for your advice.