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What version of OX is running on that Mac ? Click on the Apple icon and select About This Mac to find the version number
And what is the exact issue facing with Mail ?
Is her Mail application asking for Hotmail password ?
In Mail, look at top bar and you will see several menus like File, Edit, Mailbox etc and at last, there should be one named Window. Click it and click Connection Doctor. Run it and let me k now what it returns