This page explains how she can make Yahoo Mail her default mail application:
http://help.yahoo.com/l/us/yahoo/mail/original /settings/settings-10.html
Apart from that, you can always get the email address from a website link. Right-click on the link and choose "Copy Shortcut". In the email "To", right-click and select "Paste". Delete "mailto:" from the beginning of the address.
When you hover the mouse pointer over an email link, you can also see the address it points to in the bottom left corner of Internet Explorer, on the grey bar.