it is unusual. To complete Stefano's answer:
Usually you will rather keep the user name ( she can get a divorce, even if we do not wish that to her and wish her to enjoy her new life)
You can create a pseudonyme to morph the email, and then keep the two emails fucntional in case some emails still arrive to her old name, and believe me you will get some for the next years .
By using usermod + groupmod you desynch the two db (accounts db and pam db)
now you have a user existing on the unix system and another existing on the account db and they share the same uid and gid, thiw will create unexpected behaviour
ideally you would have avoided this situation by no using these tools.
From here, there are multiple ways to work:
-use again the tools in a reverse direction, and do one of the following:
-- create new account and transfer files, fix ownership (you can use find for uid and gid and pipe to chown the files), delete old account
-- keep the current account if she is not bohtered to keep it as a login ( I have plenty user set with a login different from their main email address) and set a pseudonyme with her new name to point to her box.
- go on with the current situation:
-- manually edit the accounts db file /home/e-smith/db/accounts to change the user name. group name is not used , but rather gid in the db so you do not have to worry about.
for info shadow / group /password allow to have multiple username groupname with same uid/gid/ For example we set www and apache with the same id. I am not sure if it would work for auth like with ssh, pop, imap, smpt etc...
AS you see there are multiple way to do, choose what seems the more feasable for you, considering the different way to do one could be chosen as a contrib for a specific need where the pseudonym workaround is not accepted, and create new account, migrate is too complexe.