Christina's book is now available for purchase from Barnes & Noble as a Nook e-book. It has also been approved for the iBookstore, but has not yet been added to the catalog. This process can apparently take quite some time (possibly months), but it is being worked on and we'll post an update as soon as we have more information.
If you've read her book and liked it, please consider posting a review either on the B&N page, Lulu.com, or as a comment here. Please also spread the word and tell others about her book as one of Christina's biggest goals was to raise awareness about both spinal cord injuries and right-to-die issues.
Edited to add: If you have an Apple device (iPod, iPad, etc.) you can download a FREE Nook app which will allow you to read the book as a Nook e-book.