If Carrie had had Type 1 diabetes as a child, she would not have surivived to adulthood. Diabetes was a terminal illness prior to 1921 and the discovery of insulin - most survived a year or less from the date of diagnosis. Insulin changed the face of diabetes from a terminal illness to a chronic one - not a cure, but a treatment.
If she developed Type 1 later in life, after the discovery of insulin, she might have done quite well for many years. I was diagnosed with Type 1 at the age of 23, which was 35 years ago (and now you all know how old I am!).
As for Rose - there is evidence that she EDITED the books, and suggested different ways to tell the story and things to add and leave out. Laura wrote the books in longhand and Rose typed them and edited as she typed. As more books were written, Rose did much less editing.
Here's a book that has correspondence and other data to back that theory:http://www.amazon.com/Becoming-Laura-Ingalls-Wilder-BIOGRAPHY/dp/082621648X/ref=sr_1_1?ie=UTF8&qid=1357044447&sr=8-1&keywords=becoming+laura+ingalls+wilder
Collections of the articles that Laura wrote for "The Missouri Ruralist" are available and definitely show her writing ability. She was not an uneducated little old lady living in the backwoods.
There is also evidence that Rose swiped at least one plot from her mother, as in her book "Let the Hurricane Roar".
The Brewsters - Tommy didn't exactly kill Clarence, but he was responsible for his death. He threw a bone at Clarence which cut him, and Clarence developed tetanus from the wound. Tommy and Clarence were half brothers, not cousins.
The Pioneer Girl website used to have tons of info, but a lot of it has been taken down. Ms. Cleaveland has announced plans to modernize the site but right now she is mostly on Facebook:http://www.facebook.com/pioneergirl
There are still lots of pictures and other info.
PS. I always though it was pretty obvious that Laura had a crush on Cap, in the beginning at least. IMHO.