I too was interested in more information on Blanche Sewell and ran across this article from 2011 which talks about her connection to Walt Disney. Thank you for the information you found. I hope you can update her information so that others can learn her story. It's interesting on your explanation on how to pronounce her last name. I would have thought it would rhyme with 'jewel'. Below is the link I found that has some nice photos of her.
http://www.disneydispatch.com/content/columns/squeak-of-the-week/2011/05-walt-disney-and-the-art-of-the-emotion-picture/