Thanks for the answers. I emailed her a book with instructions for side-loading, and she was successful. I had previously tried talking her through a shared dropbox folder setup, but she was not able to manage. I guess I will just have to email her the books one by one.
ETA: I meant to clarify, I sent her a non-DRM book from this Mobile Read library
It seems the problem she was having with the Kindle store was a conbination of her own tech cluelessness, and the Great Firewall of China. It looks like I will have to manually email her the books for side-loading. Fortunately, I have numerous omnibus books like HarryT's Sherlock Holmes one, so I won't have to deal with TOO many files...