Do you know if her email connects to the server via POP or IMAP?
If it's IMAP then all you'll need to do is open up mail on the mac, input her IMAP server details and it'll all be there. If it's POP then there are a couple of methods, but they're not as easy as it should be.
Check out this site, it should point you in the right direction:
http://guides.macrumors.com/Moving_E..._to_Apple_Mail