Amazon’s policy is: all purchased book can be read on gadget registered to one account. And Kindle (or other device) can be registered only to one account.
You can read the same books on several Kindles (or gadgets like iPhone) which are registered to your account:
http://blogkindle.com/kindle-faq/#multiple-kindles
You need to do the following steps:
1. Register all device to one account. Read the following instruction:
http://blogkindle.com/kindle-faq/#transfer
2. Downloads purchased book to your device from Archive Items
http://blogkindle.com/kindle-faq/#re-read
If you and your mom have different accounts you can:
1. lend a book for 14 days but only once:
http://blogkindle.com/2010/12/kindle-book-lending-is-here/
2. make a gift:
http://blogkindle.com/2010/11/kindle-books-become-gifts/
Discover more tips about Kindle on
http://blogkindle.com/kindle-faq
http://blogkindle.com/kindle-faq/#multiple-kindles
Source:
http://unleeshthegeek.com/2012/09/sharetransfer-ebooks-from-kindle-to-ipad/