She will not have Outlook Express.
Vista uses Windows Mail.
Or she can use Outlook which is part of Office 2007
Or download Thunderbird or Windows Live Mail or another email client.
What is she actually using at the moment?
And is the info you want for yourself using Outlook Express on XP (as you say she already is using multiple accounts on Vista)
If for you and Outlook Express then:
- Mail tab
- and fill in the details