Retriving iCloud mail through a Gmail account

My wife has an iMac which uses Mountain Lion. She has no other Apple devices, and uses iCloud for storage. She owns a Kindle HD Fire for reading and videos which can access email through Gmail. We will be travelling in a month and I need to know how to set up her Gmail account so that it can access her mail off the iCloud server. I tried to do this through the Gmail settings (Accounts and Import and Forward and POP/IMAP) but cannot get the settings for her iCloud email account to be accepted by Gmail. On the other hand, I can easily access your Gmail account on Mail.

How do I get Gmail to read her iCloud mail?