Hello, DixieGal! Much of the same free Christian fiction that is available for Kindles is also available for the Sony ereader. You can use a website like inkmesh to find the freebies. See the link below. However, even though it is free cost, it still has DRM which will be linked to your Sony account if you purchase it. Thus, if she authorizes the 505 to her own Sony account, then she won't be able to read the files.
http://inkmesh.com/free-ebooks/?site=sony
christianbook.com has over 3000+ DRM-free books, although not free cost. Some of their bestsellers are inexpensive, less than $5 per book.
http://www.christianbook.com/Christi...Enumber%5Fsold
I gave a 505 as a gift last year. I also loaded it with DRM-free ebooks that I knew the person would appreciate. I used public domain books from sites like feedbooks.com, manybooks.net and gutenberg.org.
Also, if you have a source for DRM-free Kindle books, then you could use a program like calibre to convert them to EPUB format for the 505.
Good luck! I hope your sister likes the gift!