how long was she unconcious for, not breathing? Obviously the brain requires oxygen to survive and if she was without air for some time, then obviously a lot of brain tissue will be damaged. It doesnt matter how much tissue has been damaged or died, it is what the tissues function was to the body, such as controlling breathing etc. The difference in the doctors opinions is probably due to the data presented in the MRI scan. This is an accurate way of analysing tissue. Over the next few days there should be the biggest improvements and after that the improvements become smaller and slower but go on for years. If there is dead brain tissue, it will not recover but surrounding tissue will learn to take over those missing functions as best as they can. This is why after a stroke many people lose their speech ability but it returns. My wife had a large stroke 12 weeks ago and her right leg/arm was totally paralysed. She couldnt speak at all and I was told that there would probably be no improvement. She speaks normally now, can knit using both hands and can walk using a frame. She is improving every day. It is difficult to say how well an individual will recover because we all seem to respond differently to trauma.
I really feel for you and your family, it hurts me inside to even discuss this. I will pray for you and please let me know how things are progressing.