Icloud IMAP email address

As per the article Add and manage email aliases for iCloud Mail on iCloud.com - Apple Support

Turn off, turn on or delete an alias

You can turn an email alias on or off at any time. You can also delete email aliases that you no longer want to use. While turning off an email alias is temporary, deleting it is permanent. When an alias is turned off or deleted, email sent to that alias is returned to the sender.

1. In Mail on iCloud.com, click  at the top of the Mailboxes list, then choose Settings.
2. Click Accounts, select an iCloud Mail alias in the list, then do any of the following:

• • Turn off an alias: select “Disable alias”.
  • Turn on an alias: deselect “Disable alias”.
  • Delete an alias: click “Delete alias”, then click Delete.

1. Click Done.

First check her device is added in your account , you can see the section - Remove a device from the list

in the article Check your Apple ID device list to find where you're signed in - Apple Support

See this article also to remove her Apple ID from your account About your Apple ID email addresses - Apple Support

Delete an additional email address

1. Sign in to appleid.apple.com.
2. Select Personal Information, then select Reachable At.
3. To delete one of your additional email addresses, click the Remove button next to the address.