.Net accounts

Purchased computer with Windows XP Home Edition.
Daugther set-up desktop and e-mail account under her
name. Logged onto desktop and then let friend log onto
her e-mail account. Now daughter's email account show
outstanding messages, when in fact there are none. The
outstanding messages are from her friend's account.
Question: How to delete friend's email account - would
this cure problem? None my son desktop is showing the
same signs?