I looked through the output and one problem is certainly the "MOBI markup appears to contain random bytes. Stripping." line. The sample file that I used doesn't cause that, but there are certainly enough problems with the sample that I'm not surprised that there are even more problems with the full book. Basically, it looks to me like the mobi file is formatted poorly enough that Calibre's not up to the task of converting it.
Other than the Kindle version, the only other electronic CEV that I can find for sale is for
Logos software. If your mother has an Android or iOS device, I can tell you that the Logos software (which is free to download) is easy to use, but I think you may be out of luck if you're set on finding an epub.