Any idea what she's allergic to? What foods has she been on so far that caused he allergy problems?
Raw would probably help to control things anyway, you know exactly what is going in so no guessing around what might be causing the reaction. If you feed chicken and she reacts then no more chicken, etc. Plus there is a whole lot less stuff going in, not a bunch of different meats, grains, veggies and fruit with each meal. Just meat and when you put a new meat in you are easily able to tell whether or not that is the meat that caused the reaction.
ANYway. First step would be getting her to eat meat, any meat, but start with just one source. I usually start with chicken, if you think that perhaps chicken is her allergen then try something else, rabbit or lamb might be good. Use plain meat, cut off skin if there is any, no bones. Cut the meat into small (dime sized) chunks for experimenting. offer her one chunk and see if she recognizes it as food, perhaps toss it around to see if she'll chase or grab it and eat it. If not then work on mixing it in with her food. If she gets kibble then put maybe two chunks in with 10 pieces of kibble, see if in her eating frenzy she gulps the meat down. When she eats one add another. If you ever see her directly sniff the meat and then eat it that's a strong sign she is okay with it as food. Add more pieces of meat with the kibble until she eats it all. If it's wet food then mix a good amount of meat in and see how she responds to it. If she is hesitant add more wet so that the meat is less noticeable.
Now if she decides to be difficult you'll need to be sneaky. We'll cross that bridge when you get there.
Once you can get him to eat the small chunks of meat by themselves you can slowly work up to larger chunks over time. Your goal is mouse sized chunks at least. Once he can eat those (which means he knows how to chew) start introducing organs (liver and something else like kidney, heart counts as muscle NOT organ) and bone. Good starting bones are chicken ribs or smashed up chicken necks. If he has trouble smash them and cut the meaty bone into sections that he can handle.
but for starters get him to eat small chunks. It can be easy or hard, that's up to the cat