If you check out her FAQ page from the same site it actually answers most of your questions, see below
"I thought this diet was attempting to reverse engineer a cat's natural prey. There are no Vitamin E or salmon oil capsules in a mouse, so what's the deal?
Darn it, you got me.
Seriously, you're correct that this diet is an attempt to create a mouse. But because there are usually limits to what we have to work with to accomplish that, we have to find ingredients and supplements to make up for nutrients that are lost by virtue of the fact that we're not serving fresh, whole prey and are instead buying meat, processing it (i.e., cutting it up, exposing a good deal of its surface area to air), and--for the sake of convenience and sanity--storing it. And in storing or freezing anything, you're going to lose some nutrients.
Remember too that even if you're buying a whole chicken carcass, you're still not serving a truly WHOLE carcass. The brains and eyes of a cat's prey, for example, supply a perfectly balanced ratio of Essential Fatty Acids
. Because most people aren't going be serving brains and eyes (unless you've stumbled onto an awfully resourceful and accommodating butcher), we need to do the best we can to make up for it and, hence, the salmon oil.
The Vitamin E is there to slow down oxidation of the meat which inevitably occurs once it's cut up or ground. Psyllium supplies soluble and insoluble fiber, such as might be found partly digested and in small amounts in the stomach of a cat's prey, without adding carbohydrates. Extra Taurine is there to make up for what may get lost as a result of prolonged storage or freezing of muscle or organ meat. The Winn Feline Foundation conducted an important study of raw rabbit diets for cats and learned that despite the high levels of Taurine in rabbit meat, cats fed this diet suffered from serious Taurine deficiencies. The study posited that it was possible that the bacteria in the carcass of ground rabbits or in the intestines of the cat broke down some of the Taurine. Whatever the reason, because Taurine is such a critical amino acid for cats--both for their digestion as well as their heart function--adding extra to a cat's raw diet is very wise.
Taurine is absolutely essential when it comes to steering clear of heart muscle failure in cats (dilated cardiomyopathy), and is also important in preventing feline central retinal degeneration which can cause blindness in cats.
Finally, commercially raised meats are simply not as high in many of the nutrients of free-range, naturally-raised animals that are fed a truly species-appropriate diet.
Similarly, egg yolks are added to the recipe that I use because they supply such a truly "perfect protein" and are a very nice polish to the diet, particularly if that diet is prepared using something other than perfectly fresh, species-appropriate-fed meat.
Obviously, feeding live mice, other rodents, or small birds that came from their natural environment is by far the best food for our carnivores. Since most of us aren't going to feed live, fresh prey, we are left in our kitchens to reverse engineer what they would get in that environment."
faqs - cat nutrition
The only thing not addressed is the b vitamins. But from what I understand from HUMAN nutrition (so take it with a grain of salt) You cannot overdose on B vitamins because they are water soluble and are also somewhat delicate. So it is basically insurance in case the grinding mixing freezing etc destroys alot of them. Look at most energy drinks for people and they have like 1000% percent your daily intake requirement for B vitamins in them because they are energizing.
I make some ground for my cats with this recipe and I don't use the multiglandular I add my own kidney and I stopped adding psyllium with no issues.