You've already hit on why there is a general recommendation to not switch food right away, try to keep changes to a minimum at first. Same as you do not want to give her rabies vaccinations with all her other shots, just to avoid overwhelming a young system with what might be too much too soon all at once.
Think as well, hopefully you chose a reputable breeder who has chosen the best foods for her dogs and knows what works for them. The breeder is providing you with the health test results on the parents, the ones recommended for that breed. As well the breeder is involved the breed club and shows, or tests, or trials her dogs, whatever it is that breed is known for. If you decided this is the right breeder then isn't the food she uses good too?
I like this site (link below) for learning about dog food ingredients and how to read labels. I know you want to go raw but understanding the make up of the breeder's food might be illuminating. For instance you mention corn, but there is nothing wrong with corn in the right amounts and in the proper place in the ingredient list. And by-products, LOL, lots of raw feeders feed what we consider to be by-products such as offal and chicken feet.
http://www.dogfoodproject.com/