As for renaming the domain, it should be fine as long as you are in 2003 Native mode for for domain.
You should keep exchange on a member server instead of a domain controller. I would demote the new server to a member server and install exchange and migrate the mailboxes and make the old exchange server a backup DC.
As far as Ghosting, you can ghost a server but you need to make the image before you make it a member of the domain.
The bounce back messages is a little mind boggling. I would enable message tracking and see where the message is going when sending it from her account and also the queue in ESM.