I would suggest calling your public library's reference dept. They will steer you to both paper and online sources that will be just what she needs. Don't drive yourself nuts trying to do this yourself when expert researchers are just a phone call or an email away.
(And if your own public library is inadequate, contact the nearest large one. Reference advice is almost always NOT dependent on residency -- we will offer assistance to anyone who asks for it.)
COUNTLESS books, articles and dissertations have been written about Walt Disney and the Disney company over the past 75 years or so. There is no shortage of factual material out there, though a fair amount of the digitized things are going to be behind a paywall. That's where your library is likely to be able to help; as most systems now offer password access to paid databases for their resident users, and interlibrary loan to just about everyone else.