Inflammatory Bowel Desease

My poor little dog has just been diagnosed with Inflammed bowels and is on Purina HA dry food. She was ok with it initially but now refuses to eat it no matter how hungry she is..caught her eating tissues last night from the box!!!!!! The poor little thing is wasting away before our eyes has lost so much weight and its heartbreaking to watch. I'm not allowed to give her any other food other than the Purina so basically we are starving her to death. I want her to get better of course and if the vets say this is what she must have then so be it....but at what cost..to watch your dog slowly wither away from starvation.