NO
iCloud is but a conduit to have files in iCloud so that other computers signed into the same Account Account can access those files
To Backup your wife's data , it is best to use Time Machine Backup Utilities
Transfer to a new Mac with Migration Assistan
Emails are a bit more complicated and is 100% dependent on the email account
Email accounts that use the newer and most commonly used Protocol >>> IMAP
The emails are actually On the email account server(s) and once the new computer is setup
Just Add the email account >> Add email accounts in Mail on Mac
Should the email account use the Older and less used Protocol >> POP
That is best left to TM Backup Utilities