Well, sudden changes in diet can affect the GI tract, so I would start very modestly with perhaps a teaspoon or two if you decide to do it.
You want to keep the protein calories at about 40% or more in order to build muscle back up. And something like Wellness Turkey & Giblet might do that ratio and be low carb without having to fuss with duck fat.
What vets may do when re-feeding is frequent small meals. In a starvation case, they may use a high fiber product because the animal will eat ravenously and too much, too fast can provoke vomiting (among other things) which defeats the process.
As you establish good glucose control, any extra calories consumed (fat, protein, or carbohydrate) can be stored.