The little girl running to the library (modern day) to check out a book is Michael Landon's daughter Shawna.
There are two pictures hanging on the wall of the publishers office. The one on the right is Laura Ingalls Wilder. The other may possibly be her sister Carrie.
When Laura is reading her novel to Almanzo, after she has just got done writing it, Melissa Gilbert is reciting the exact last paragraph in Laura Ingalls Wilder's real Little House In the Big Woods.
In real life, Laura didn't write her first book until c. 1914, called "Pioneer Girl", which would have been over 25 years after the time setting for "Once Upon A Time". The first "Little House On The Prairie" book was not published until 1932, when she was in her early 60's. She was encouraged to write her stories by her daughter Rose Wilder Lane, who was already successful in publishing.
The book that Shawna grabs in the library is one of the actual Little house books.